Communication system

ABSTRACT

The present invention has an object to provide a communication system capable of appropriately providing services while improving a data rate using carrier aggregation. In Step ST 1408 , of a cell 1  and a cell 2  of a base station A, RRC connection is established between the cell 1  and a UE, and the cell 1  becomes a primary cell (PCell). Then, in Step ST 1418 , the cell 1  determines to configure the cell 2  as a secondary cell (SCell) to be aggregated with the own cell. Then, the cell 1  notifies the UE of the above in Step ST 1419 . Upon this notification, the operation of restricting access to the cell 2  from the UE is stopped by an MME, and thereafter, communication between the UE and the cell 2  is started in Step ST 1422.

TECHNICAL FIELD

The present invention relates to a communication system in which a basestation device performs radio communication with a plurality ofcommunication terminal devices.

BACKGROUND ART

Commercial service of a wideband code division multiple access (W-CDMA)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, high speed downlink packetaccess (HSDPA) service for achieving higher-speed data transmissionusing a downlink has been offered by adding a channel for packettransmission (high speed-downlink shared channel (HS-DSCH)) to thedownlink (dedicated data channel, dedicated control channel). Further,in order to increase the speed of data transmission in an uplinkdirection, service of a high speed uplink packet access (HSDPA) systemhas been offered. W-CDMA is a communication system defined by the 3rdgeneration partnership project (3GPP) that is the standard organizationregarding the mobile communication system, where the specifications ofRelease 10 version are produced.

Further, new communication systems referred to as long term evolution(LTE) regarding radio areas and system architecture evolution (SAE)regarding the overall system configuration including a core network(merely referred to as network as well) as communication systemsindependent of W-CDMA is studied in 3GPP. This communication system isalso referred to as 3.9 generation (3.9 G) system.

In the LTE, an access scheme, a radio channel configuration and aprotocol are totally different from those of the current W-CDMA(HSDPA/HSUPA). For example, as to the access scheme, code divisionmultiple access is used in the W-CDMA, whereas in the LTE, orthogonalfrequency division multiplexing (OFDM) is used in a downlink directionand single career frequency division multiple access (SC-FDMA) is usedin an uplink direction. In addition, the bandwidth is 5 MHz in theW-CDMA, while in the LTE, the bandwidth can be selected from 1.4 MHz, 3MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz per base station. Further,differently from the W-CDMA, circuit switching is not provided but apacket communication system is only provided in the LTE.

The LTE is defined as a radio access network independent of the W-CDMAnetwork because its communication system is configured by a new corenetwork different from a core network (general packet radio service:GPRS) of the W-CDMA. Therefore, for differentiation from the W-CDMAcommunication system, a base station that communicates with a userequipment (UE) and a radio network controller that transmits/receivescontrol data and user data to/from a plurality of base stations arereferred to as an E-UTRAN NodeB (eNB) and an evolved packet core (EPC)or access gateway (aGW), respectively, in the LTE communication system.

Unicast service and evolved multimedia broadcast multicast service(E-MBMS service) are provided in this LTE communication system. TheE-MBMS service is broadcast multimedia service, which is merely referredto as MBMS in some cases. Bulk broadcast contents such as news, weatherforecast and mobile broadcast are transmitted to a plurality of userequipments. This is also referred to as point to multipoint service.

Non-Patent Document 1 (Chapter 4) describes the current decisions by3GPP regarding an overall architecture in the LTE system. The overallarchitecture is described with reference to FIG. 1. FIG. 1 is a diagramillustrating the configuration of the LTE communication system. Withreference to FIG. 1, the evolved universal terrestrial radio access(E-UTRAN) is composed of one or a plurality of base stations 102,provided that a control protocol for a user equipment 101 such as aradio resource control (RRC) and user planes such as a packet dataconvergence protocol (PDCP), radio link control (RLC), medium accesscontrol (MAC) and physical layer (PHY) are terminated in the basestation 102.

The base stations 102 perform scheduling and transmission of a pagingsignal (also referred to as paging messages) notified from a mobilitymanagement entity (MME) 103. The base stations 102 are connected to eachother by means of an X2 interface. In addition, the base stations 102are connected to an evolved packet core (EPC) by means of an S1interface. More specifically, the base station 102 is connected to themobility management entity (MME) 103 by means of an S1_MME interface andconnected to a serving gateway (S-GW) 104 by means of an S1_U interface.

The MME 103 distributes the paging signal to a plurality of or a singlebase station 102. In addition, the MME 103 performs mobility control ofan idle state. When the user equipment is in the idle state and anactive state, the MME 103 manages a list of tracking areas.

The S-GW 104 transmits/receives user data to/from one or a plurality ofbase stations 102. The S-GW 104 serves as a local mobility anchor pointin handover between base stations. Moreover, a PDN gateway (P-GW) isprovided in the EPC, which performs per-user packet filtering and UE-IDaddress allocation.

The control protocol RRC between the user equipment 101 and the basestation 102 performs broadcast, paging, RRC connection management andthe like. The states of the base station and the user equipment in RRCare classified into RRC_Idle and RRC_CONNECTED. In RRC_IDLE, public landmobile network (PLMN) selection, system information (SI) broadcast,paging, cell re-selection, mobility and the like are performed. InRRC_CONNECTED, the user equipment has RRC connection, is capable oftransmitting/receiving data to/from a network, and performs, forexample, handover (HO) and measurement of a neighbour cell.

The current decisions by 3GPP regarding the frame configuration in theLTE system described in Non-Patent Document 1 (Chapter 5) are describedwith reference to FIG. 2. FIG. 2 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 2, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).

Multiplexing of channels for multimedia broadcast multicast servicesingle frequency network (MBSFN) and for non-MBSFN is performed on aper-subframe basis. MBSFN transmission is a simulcast transmissiontechnique realized by simultaneous transmission of the same waveformsfrom a plurality of cells. The MBSFN transmission from a plurality ofcells in the MBSFN area is seen as a single transmission by a userequipment. The MBSFN is a network that supports such MBSFN transmission.Hereinafter, a subframe for MBSFN transmission is referred to as MBSFNsubframe.

Non-Patent Document 2 describes a signaling example when MBSFN subframesare allocated. FIG. 3 is a diagram illustrating the configuration of theMBSFN frame. With reference to FIG. 3, a radio frame including the MBSFNsubframes is allocated per radio frame allocation period. The MBSFNsubframe is a subframe allocated for the MBSFN in a radio frame definedby the allocation period and the allocation offset (radio frameallocation offset), and serves to transmit multimedia data. The radioframe satisfying Equation (1) below is a radio frame including the MBSFNsubframes.SFN mod radioFrameAllocationPeriod=radioFrameAllocationOffset  (1)

The MBSFN subframe is allocated with six bits. The leftmost bit definesthe MBSFN allocation for the second subframe (#1). The second bit, thirdbit, fourth bit, fifth bit, and sixth-bit define the MBSFN allocationfor the third subframe (#2), fourth subframe (#3), seventh subframe(#6), eighth subframe (#7), and ninth subframe (#8), respectively. Thecase where the bit indicates “one” represents that the correspondingsubframe is allocated for the MBSFN.

Non-Patent Document 1 (Chapter 5) describes the current decisions by3GPP regarding the channel configuration in the LTE system. It isassumed that the same channel configuration is used in a closedsubscriber group cell (CSG cell) as that of a non-CSG cell. Physicalchannels are described with reference to FIG. 4. FIG. 4 is a diagramillustrating physical channels used in the LTE communication system.

With reference to FIG. 4, a physical broadcast channel (PBCH) 401 is adownlink channel transmitted from the base station 102 to the userequipment 101. A BCH transport block is mapped to four subframes withina 40 ms interval. There is no explicit signaling indicating 40 mstiming. A physical control format indicator channel (PCFICH) 402 istransmitted from the base station 102 to the user equipment 101. ThePCFICH notifies the number of OFDM symbols used for PDCCHs from the basestation 102 to the user equipment 101. The PCFICH is transmitted in eachsubframe.

A physical downlink control channel (PDCCH) 403 is a downlink channeltransmitted from the base station 102 to the user equipment 101. ThePDCCH notifies the resource allocation of DL-SCH (downlink sharedchannel that is one of the transport channels shown in FIG. 5 describedbelow) and PCH (paging channel that is one of the transport channelsshown in FIG. 5), and HARQ information related to DL-SCH. The PDCCHcarries an uplink scheduling grant. The PDCCH carries acknowledgement(Ack)/negative acknowledgement (Nack) that is a response signal touplink transmission. The PDCCH is referred to as an L1/L2 control signalas well.

A physical downlink shared channel (PDSCH) 404 is a downlink channeltransmitted from the base station 102 to the user equipment 101. ADL-SCH (downlink shared channel) that is a transport channel and a PCHthat is a transport channel are mapped to the PDSCH. A physicalmulticast channel (PMCH) 405 is a downlink channel transmitted from thebase station 102 to the user equipment 101. A multicast channel (MCH)that is a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) 406 is an uplink channeltransmitted from the user equipment 101 to the base station 102. ThePUCCH carries Ack/Nack that is a response signal to downlinktransmission. The PUCCH carries a channel quality indicator (CQI)report. The CQI is quality information indicating the quality ofreceived data or channel quality. In addition, the PUCCH carries ascheduling request (SR). A physical uplink shared channel (PUSCH) 407 isan uplink channel transmitted from the user equipment 101 to the basestation 102. A UL-SCH (uplink shared channel that is one of thetransport channels shown in FIG. 5) is mapped to the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) 408 is a downlinkchannel transmitted from the base station 102 to the user equipment 101.The PHICH carries Ack/Nack that is a response to uplink transmission. Aphysical random access channel (PRACH) 409 is an uplink channeltransmitted from the user equipment 101 to the base station 102. ThePRACH carries a random access preamble.

A downlink reference signal is a known symbol in a mobile communicationsystem. The physical layer measurement objects of a user equipmentinclude reference symbol received power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)are described with reference to FIG. 5. FIG. 5 is a diagram illustratingtransport channels used in the LTE communication system. Part (A) ofFIG. 5 shows mapping between a downlink transport channel and a downlinkphysical channel. Part (B) of FIG. 5 shows mapping between an uplinktransport channel and an uplink physical channel.

Downlink transport channels are described. A broadcast channel (BCH) isbroadcast to the entire coverage of a base station (cell). The BCH ismapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH enables broadcast to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. The PCH is required to broadcast tothe entire coverage of the base station (cell). The PCH is mapped tophysical resources such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of MBMSservice (MTCH and MCCH) in multi-cell transmission. The MCH supportssemi-static resource allocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH). The UL-SCH supports dynamic orsemi-static resource allocation. The UL-SCH is mapped to the physicaluplink shared channel (PUSCH).

A random access channel (RACH) shown in part (B) of FIG. 5 is limited tocontrol information. The RACH involves a collision risk. The RACH ismapped to the physical random access channel (PRACH).

The HARQ is described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest and error correction (forward error correction). The HARQ has anadvantage that error correction functions effectively by retransmissioneven for a channel whose communication quality changes. In particular,it is also possible to achieve further quality improvement inretransmission through combination of the reception results of the firsttransmission and the reception results of the retransmission.

An example of the retransmission method is described. In a case wherethe receiver fails to successfully decode the received data, in otherwords, in a case where a cyclic redundancy check (CRC) error occurs(CRC=NG), the receiver transmits “Nack” to the transmitter. Thetransmitter that has received “Nack” retransmits the data. In a casewhere the receiver successfully decodes the received data, in otherwords, in a case where a CRC error does not occur (CRC=OK), the receivertransmits “AcK” to the transmitter. The transmitter that has received“Ack” transmits the next data.

Examples of the HARQ system include chase combining. In chase combining,the same data is transmitted in the first transmission andretransmission, which is the system for improving gains by combining thedata of the first transmission and the data of the retransmission inretransmission. This is based on the idea that correct data is partiallyincluded even if the data of the first transmission contains an error,and highly accurate data transmission is enabled by combining thecorrect portions of the first transmission data and the retransmissiondata. Another example of the HARQ system is incremental redundancy (IR).The IR is aimed to increase redundancy, where a parity bit istransmitted in retransmission to increase the redundancy by combiningthe first transmission and retransmission, to thereby improve thequality by an error correction function.

A logical channel described in Non-Patent Document 1 (Chapter 6) isdescribed with reference to FIG. 6. FIG. 6 is a diagram illustratinglogical channels used in an LTE communication system. Part (A) of FIG. 6shows mapping between a downlink logical channel and a downlinktransport channel. Part (B) of FIG. 6 shows mapping between an uplinklogical channel and an uplink transport channel.

A broadcast control channel (BCCH) is a downlink channel for broadcastsystem control information. The BCCH that is a logical channel is mappedto the broadcast channel (BCH) or downlink shared channel (DL-SCH) thatis a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingchanges of the paging information and system information. The PCCH isused when the network does not know the cell location of a userequipment. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between user equipments and a base station. The CCCH is usedin a case where the user equipments have no RRC connection with thenetwork. In a downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In an uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a channel for point-to-pointtransmission of the dedicated control information between a userequipment and a network. The DCCH is used when a user equipment is inRRC connection. The DCCH is mapped to the uplink shared channel (UL-SCH)in uplink and mapped to the downlink shared channel (DL-SCH) indownlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of the user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

GCI represents a global cell identity. A closed subscriber group cell(CSG cell) is introduced in the LTE, long term evolution advanced(LTE-A) described below, and universal mobile telecommunication system(UMTS). The CSG is described below (see Chapter 3.1 of Non-PatentDocument 3). The closed subscriber group cell (CSG cell) is a cell inwhich subscribers who are allowed to use can be specified by an operator(hereinafter, referred to as “cell for specific subscribers” in somecases).

The specified subscribers are allowed to access one or more cells of apublic land mobile network (PLMN). One or more cells in which thespecified subscribers are allowed access are referred to as “CSGcell(s)”. Note that access is restricted in the PLMN. The CSG cell ispart of the PLMN that broadcasts a specific CSG indication (CSG ID;CSG-ID) and broadcasts “TRUE” by CSG indication. The authorized membersof the subscriber group who have registered in advance access the CSGcells using the CSG-ID that is the access permission information.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in a mobile communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier.

The locations of user equipments are tracked based on an area composedof one or more cells. The locations are tracked for enabling tracking ofthe locations of user equipments and calling (calling of userequipments) even in an idle state. An area for tracking locations ofuser equipments is referred to as a tracking area.

A CSG whitelist is a list that may be stored in a universal subscriberidentity module (USIM) in which all CSG IDs of the CSG cells to whichthe subscribers belong are recorded. Alternatively, the CSG whitelist ismerely referred to as whitelist or is referred to as an allowed CSG listin some cases. The MME performs access control for the UEs accessingthrough CSG cells (see Chapter 4.3.1.2 of Non-Patent Document 9).Specific examples of the access by user equipments include attach,combined attach, detach, service request, and tracking area updateprocedure (see Chapter 4.3.1.2 of Non-Patent Document 9).

Service types of a user equipment in an idle state are described below(see Chapter 4.3 of Non-Patent Document 3). The service types of a userequipment in an idle state are classified into a limited service (alsoreferred to as closed service), a normal service, and an operatorservice. The limited service includes emergency calls, an earthquake andtsunami warning system (ETWS), and a commercial mobile alert system(CMAS) on an acceptable cell described below. The normal service (alsoreferred to as standard service) is the service for public use on asuitable cell described below. The operator service is the service foroperators only on a reserved cell described below.

A “suitable cell” is described below. The “suitable cell” is a cell onwhich a UE may camp to obtain a normal service. Such a cell shallfulfill the following conditions (1) and (2).

(1) The cell is part of the selected PLMN or the registered PLMN, orpart of the PLMN of an “equivalent PLMN list”.

(2) According to the latest information provided by a non-access stratum(NAS), the cell shall further fulfill the following conditions (a) to(d):

(a) the cell is not a barred cell;

(b) the cell is part of a tracking area (TA), not part of the list of“forbidden LAs for roaming”, where the cell needs to fulfill (1) above;

(c) the cell shall fulfill the cell selection criteria; and

(d) for a cell specified as CSG cell by system information (SI), theCSG-ID is part of a “CSG whitelist” of the UE (contained in the CSGwhitelist of the UE).

An “acceptable cell” is described below. This is the cell on which a UEmay camp to obtain limited service. Such a cell shall fulfill all therequirements of (1) and (2) below.

(1) The cell is not a barred cell. (2) The cell fulfills the cellselection criteria.

“Barred cell” is shown in the system information. “Reserved cell” isshown in the system information.

“Camping on a cell” represents the state where a UE has completed thecell selection/reselection process and the UE has selected a cell formonitoring the system information and paging information. A cell onwhich the UE camps is referred to as “serving cell” in some cases.

Base stations referred to as Home-NodeB (Home-NB; HNB) and Home-eNodeB(Home-eNB; HeNB) are studied in 3GPP. HNB/HeNB is a base station for,for example, household, corporation or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 4 discloses three different modes ofthe access to the HeNB and HNB. Specifically, those are an open accessmode, a closed access mode and a hybrid access mode.

The respective modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a cell where only CSG members are allowedaccess. In the hybrid access mode, non-CSG members are allowed access atthe same time. In other words, a cell in the hybrid access mode (alsoreferred to as hybrid cell) is the cell that supports both the openaccess mode and the closed access mode.

According to 3GPP, there is a range of PCIs in all physical cellidentities (PCIs), which is reserved by the network for use by CSG cells(see Chapter 10.5.1.1 of Non-Patent Document 1). Splitting the range ofPCIs is referred to PCI-split as times. The PCI split information isbroadcast in the system information from the base station to the userequipments being served thereby. Non-Patent Document 5 discloses thebasic operation of a user equipment using PCI split. The user equipmentthat does not have the PCI split information needs to perform cellsearch using all PCIs (for example, using all 504 codes). On the otherhand, the user equipment that has the PCI split information is capableof performing cell search using the PCI split information.

Further, specifications standard of long term evolution advanced (LTE-A)as Release 10 are pursued in 3GPP (see Non-Patent Document 6 andNon-Patent Document 7).

As to the LTE-A system, it is studied that a relay and a relay node (RN)are supported for achieving a high data rate, high cell-edge throughput,new coverage area, and the like. The relay node is wirelessly connectedto the radio-access network via a donor cell (Donor eNB; DeNB). Thenetwork (NW)-to-relay node link shares the same frequency band with thenetwork-to-UE link within the range of the donor cell. In this case, theUE in Release 8 can also be connected to the donor cell. The linkbetween a donor cell and a relay node is referred to as a backhaul link,and the link between the relay node and the UE is referred to as anaccess link.

As the method of multiplexing a backhaul link in frequency divisionduplex (FDD), the transmission from DeNB to RN is carried out in adownlink (DL) frequency band, and the transmission from RN to DeNB iscarried out in an uplink (UL) frequency band. As the method of dividingresources in relays, a link from DeNB to RN and a link from RN to UE aretime-division multiplexed in one frequency band, and a link from RN toDeNB and a link from UE to RN are also time-division multiplexed in onefrequency band. This enables to prevent, in a relay, the transmission ofthe relay from interfering with the reception of the own relay.

Not only a normal eNB (macro cell) but also so-called local nodes suchas pico eNB (pico cell), HeNB/HNB/CSG cell, node for hotzone cells,relay node, and remote radio head (RRH) are studied in 3GPP.

The frequency bands (hereinafter, referred to as “operating bands” insome cases) usable for communication have been predetermined in the LTE.Non-Patent Document 8 describes the frequency bands. In the frequencydivision duplex (FDD) communication, a frequency band for downlink(hereinafter, referred to as “downlink frequency band” in some cases)and a frequency band for uplink (hereinafter, referred to as “uplinkfrequency band” in some cases) that is paired with the downlinkfrequency band have been predetermined, where the uplink frequency banddiffers from the downlink frequency band. This is because the downlinkand uplink are necessarily required for conventional communication suchas voice communication so that transmission and reception are enabled atthe same time by splitting the frequencies between downlink and uplinkin the FDD.

In the FDD, a default value of an interval (TX-RX frequency separation)between a carrier frequency of resources for use in downlink(hereinafter, referred to as “downlink carrier frequency” in some cases)and a carrier frequency of resources for use in uplink (hereinafter,referred to as “uplink carrier frequency” in some cases) is determinedper frequency band. Non-Patent Document 8 describes a default value atthe TX-RX frequency separation.

In the LTE, a cell broadcasts, to UEs being served thereby, thefrequency band information and uplink carrier frequency deployed by theown cell as broadcast information. Specifically, the frequency bandinformation is included in the SIB1. The uplink carrier frequency isincluded in the SIB2. In a case where the uplink carrier frequency isnot included in the SIB2, the uplink carrier frequency is derived fromthe downlink carrier frequency using the default value at the TX-RXfrequency separation. The UE is capable of recognizing the downlinkcarrier frequency through cell selection or reselection and is capableof obtaining the frequency band and uplink carrier frequency deployed bythe cell through reception of the broadcast information from the cell.

As disclosed in Non-Patent Document 1, the development of “long termevolution advanced (LTE-A)” specifications as Release 10 is purused in3GPP.

Carrier aggregation (CA) is studied in the LTE-A system, in which two ormore component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

A Release 8 or 9-compliant UE, which supports LTE, is capable oftransmission and reception on only the CC corresponding to one servingcell. On the other hand, it is conceivable that a Release 10-compliantUE may have the capability of transmission and reception, onlyreception, or only transmission on the CCs corresponding to a pluralityof serving cells at the same time.

Each CC employs the configuration of Release 8 or 9, and the CA supportscontiguous CCs, non-contiguous CCs, and CCs in different frequencybandwidths. The UE cannot configure the number of uplink CCs (UL CCs)equal to or more than the number of downlink CCs (DL CCs). The CCsconfigured by the same eNBs do not need to provide the same coverage.The CC is compatible with Release 8 or 9.

In CA, an independent HARQ entity is provided per serving cell in uplinkas well as downlink. A transport block is generated per TTI for eachserving cell. Each transport block and HARQ retransmission are mapped toa single serving cell.

In a case where CA is configured, a UE has single RRC connection with aNW. In RRC connection, one serving cell provides NAS mobilityinformation and security input. This cell is referred to as primary cell(PCell). In downlink, a carrier corresponding to PCell is a downlinkprimary component carrier (DL PCC). In uplink, a carrier correspondingto PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a pair of a PCell and aserving cell, in accordance with the UE capability. In downlink, acarrier corresponding to SCell is a downlink secondary component carrier(DL SCC). In uplink, a carrier corresponding to SCell is an uplinksecondary component carrier (UL SCC).

A pair of one PCell and a serving cell configured by one or more SCellsis configured for one UE.

In each SCell, a UE is capable of using resources for uplink (UL) inaddition to resources for downlink (DL). The number of DL SCCs is equalto or more than the number of UL SCCs. No SCell is used for onlyresources for UL. Each resource for UL belongs to only one serving cellfor one UE. The number of serving cells depends on the UE capability.

The PCell is changed through only a HO procedure. The PCell is used fortransmission of PUCCH. The PUCCH for HARQ of the DL-SCH without UL-SCHis transmitted through only UL PCC. Differently from Scells, the PCellis not de-activated.

Re-establishment is triggered when the PCell results in a radio linkfailure (RLF). Re-establishment is not triggered in a case of SCells.The NAS information is obtained from the PCell.

The SCells are reconfigured, added, or removed through RRC. Also inhandover within the LTE, the SCells used together with a target PCellare added, removed, or reconfigured through RRC.

In a case of SCell addition, dedicated RRC signaling is used to transmitthe all system information (SI) required for the SCell. That is,addition is performed in a connected mode, and the UE does not have toreceive the SI broadcast from the SCell.

It is studied that a PCell notifies user equipments of SCelladdition/modification using “RRC Connection Reconfiguration message” ofdedicated RRC signaling (see Non-Patent Document 2). It is studied thatSCell release is notified UEs by a PCell using “RRC ConnectionReconfiguration message” of dedicated RRC signaling or is triggered by“RRC Connection re-establishment” (see Non-Patent Document 2). “RRCConnection Reconfiguration message” of dedicated RRC signaling contains“SCell To AddModList” and “SCell To ReleaseList”.

In each cell, the SIB2 represents a carrier frequency of a resource foruplink.

Non-Patent Document 10 discloses that a CSG indication and a CSG-ID canbe configured per cell (CC). However, Non-Patent Document 10 does notdescribe the method of notifying user equipments of the configurationcontent. Also, Non-Patent Document 10 does not pose a problem with therelationship between the CSG to which the SCell belongs and the CSG towhich the user equipment belongs, and does not disclose a solutionthereto.

Non-Patent Document 2 discloses that a PCell notifies user equipments ofSCell addition/modification using “RRC Connection Reconfigurationmessage” of dedicated RRC signaling. “RRC Connection Reconfigurationmessage” of dedicated RRC signaling regarding SCelladdition/modification does not contain a CSG indication and a CSG-ID.Non-Patent Document 2 does not describe the method of configuring theCSG indication and CSG-ID per SCell and the method of notifying userequipments of the configuration content. Also, Non-Patent Document 2does not pose a problem with the relationship between the CSG to whichthe SCell belongs and the CSG to which the user equipment belongs, anddoes not disclose a solution thereto.

PRIOR ART DOCUMENTS Non-Patent Documents

Non-Patent Document 1: 3GPP TS 36.300 V10.2.0

Non-Patent Document 2: 3GPP TS 36.331 V10.0.0

Non-Patent Document 3: 3GPP TS 36.304 V10.0.0 Chapter 3.1, Chapter 4.3,Chapter 5.2.4

Non-Patent Document 4: 3GPP S1-083461

Non-Patent Document 5: 3GPP R2-082899

Non-Patent Document 6: 3GPP TR 36.814 V9.0.0

Non-Patent Document 7: 3GPP TR 36.912 V9.3.0

Non-Patent Document 8: 3GPP TS 36.101 V10.0.0

Non-Patent Document 9: 3GPP TR 23.830 V9.0.0

Non-Patent Document 10: 3GPP R2-104041

SUMMARY OF INVENTION Problem to be Solved by the Invention

It is considered that the LTE-A system supports frequency bandwidthslarger than the frequency bandwidths of the LTE system, specifically,frequency bandwidths up to 100 MHz for improving a data rate. Carrieraggregation (CA) is studied as one method of supporting those. Incarrier aggregation, a pair of serving cells is formed of the PCell andSCell for a user equipment.

As described above, Non-Patent Document 2 and Non-Patent Document 10 donot describe the method of notifying user equipments of the CSGindication and CSG-ID per SCell. In addition, Non-Patent Document 2 andNon-Patent Document 10 do not describe the relationship between the CSGto which the SCell belongs and the CSG to which the user equipmentbelongs. As a result, the operation of the communication system cannotbe determined uniquely, leading to a problem that services cannot beprovided appropriately.

An object of the present invention is to provide a communication systemcapable of appropriately providing services while improving a data rateusing carrier aggregation.

Means to Solve the Problem

A communication system according to the present invention includes acommunication terminal device, a base station device configured toperform radio communication with the communication terminal device, anda host node device that restricts the connection between thecommunication terminal device and the base station device. The basestation device includes a plurality of cells formed of componentcarriers having different frequencies, which aggregates two or morecells of the plurality of cells and transmits and receives componentcarriers of the aggregated cells in parallel to perform radiocommunication with the communication terminal device. The plurality ofcells include a cell for specific subscribers that specifies aconnectable communication terminal device. Upon establishment of radioconnection between any one of the plurality of cells and thecommunication terminal device, the connected cell configures any ofother cells as an aggregable cell that is allowed to be aggregated withthe own cell, the connected cell being a cell in which radio connectionwith the communication terminal device has been established. When theaggregable cell is configured by the connected cell, the host nodedevice stops an operation of restricting access to the aggregable cell,and the communication terminal device stops an operation of restrictingaccess to the aggregable cell based on cell information beinginformation related to the cell for specific subscribers held inadvance.

Further, a communication system according to the present inventionincludes a communication terminal device, a base station deviceconfigured to perform radio communication with the communicationterminal device, and a host node device that restricts the connectionbetween the communication terminal device and the base station device.The base station device provides a plurality of cells formed ofcomponent carriers having different frequencies, which aggregates two ormore cells of the plurality of cells and transmits and receivescomponent carriers of the aggregated cells in parallel to perform radiocommunication with the communication terminal device. The plurality ofcells include a cell for specific subscribers that specifies aconnectable communication terminal device. Upon establishment of radioconnection between any one of the plurality of cells and thecommunication terminal device, the connected cell selects any one of theother cells as a candidate cell being a candidate for aggregable cellthat is allowed to be aggregated with the own cell and notifies thecommunication terminal device of information related to the selectedcandidate cell, the connected cell being a cell in which radioconnection with the communication terminal device has been established.Upon notification of the information related to the candidate cell fromthe connected cell, the communication terminal device judges whether ornot access to the candidate cell is allowed based on cell informationrelated to the cell for specific subscribers held in advance andnotifies the connected cell of the judgment results. When judging thataccess to the candidate cell is allowed based on the judgment resultsnotified from the communication terminal device, the connected cellconfigures the candidate cell as the aggregable cell. When theaggregable cell is configured by the connected cell, the host nodedevice stops an operation of restricting access to the aggregable cell.

Effects of the Invention

According to the communication system of the present invention, theoperation as a communication system can be stabilized while improving adata rate using carrier aggregation, which enables to appropriatelyprovide services.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of an MBSFN frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIG. 5 is a diagram illustrating transport channels used in the LTEcommunication system.

FIG. 6 is a diagram illustrating logical channels used in the LTEcommunication system.

FIG. 7 is a block diagram showing the overall configuration of an LTEmobile communication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment(user equipment 71 of FIG. 7) according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station(base station 72 of FIG. 7) according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME (MME unit73 of FIG. 7) according to the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGW 74shown in FIG. 7 that is a HeNBGW according to the present invention.

FIG. 12 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 13 is a diagram showing the conception of CA.

FIG. 14 is a diagram showing an example of a sequence of a communicationsystem in a second embodiment.

FIG. 15 is a diagram showing an example of a sequence of a communicationsystem in a first modification of the second embodiment.

FIG. 16 is a diagram showing an example of a sequence of a communicationsystem in a third embodiment.

FIG. 17 is a diagram showing another example of the sequence of thecommunication system in the third embodiment.

FIG. 18 is a diagram showing an example of a sequence of a communicationsystem in a fourth embodiment.

FIG. 19 is a diagram showing another example of the sequence of thecommunication system in the fourth embodiment.

FIG. 20 is a diagram showing an example of a sequence of a communicationsystem in a fifth embodiment.

FIG. 21 is a diagram showing an example of a sequence of a communicationsystem in a first modification of the fifth embodiment.

FIG. 22 is a diagram showing an example of a sequence of a communicationsystem in a sixth embodiment.

FIG. 23 is a diagram showing a sequence of a communication systemregarding a handover method from an eNB or HeNB to a CSG cell or hybridcell, which is disclosed in Non-Patent Document 1.

FIG. 24 is a diagram showing an example of a sequence of a communicationsystem in an eighth embodiment.

FIG. 25 is a diagram showing an example of a sequence of a communicationsystem in a first modification of the eighth embodiment.

FIG. 26 is a diagram showing an example of a sequence of a communicationsystem in a second modification of the eighth embodiment.

FIG. 27 is a diagram showing an example of a sequence of a communicationsystem in a third modification of the eighth embodiment.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEmobile communication system, which is currently under discussion of3GPP. Currently, an overall system configuration including closedsubscriber group (CSG) cells (Home-eNodeBs (Home-eNB; HeNB) of E-UTRAN,Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB (eNB) of E-UTRAN,NodeB (NB) of UTRAN, and BSS of GERAN) is studied in 3GPP and, as toE-UTRAN, the configuration as shown in FIG. 7 is proposed (see Chapter4.6.1 of Non-Patent Document 1).

FIG. 7 is described. A user terminal device (hereinafter, referred to as“user equipment” or “UE”) 71 is capable of performing radiocommunication with a base station device (hereinafter, referred to as“base station”) 72 and transmits/receives signals through radiocommunication. The user terminal device is equivalent to a communicationterminal device. The base stations 72 are classified into an eNB 72-1that is a macro cell and a Home-eNB 72-2 that is a local node. The eNB72-1 is equivalent to a large-scale base station device and has arelatively large-scale coverage as the coverage in a range in whichcommunication is allowed with the user equipment UE 71. The Home-eNB72-2 is equivalent to a small-scale base station device and has arelatively small-scale coverage as the coverage.

The eNB 72-1 is connected to an MME/S-GW unit (hereinafter, referred toas an “MME unit” in some cases) 73 including an MME, S-GW or MME andS-GW through an S1 interface, and control information is communicatedbetween the eNB 72-1 and the MME unit 73. A plurality of MME units 73may be connected to one eNB 72-1. The eNBs 72-1 are connected to eachother by means of an X2 interface, and control information iscommunicated between the eNBs 72-1.

The Home-eNB 72-2 is connected to the MME unit 73 by means of an S1interface, and the control information is communicated between theHome-eNB 72-2 and the MME unit 73. A plurality of Home-eNBs 72-2 areconnected to one MME unit 73. Also, the Home-eNBs 72-2 are connected tothe MME units 73 through a Home-eNB Gateway (HeNBGW) 74. The Home-eNBs72-2 are connected to the HeNBGW 74 by means of the S1 interface, andthe HeNBGW 74 is connected to the MME units 73 through an S1 interface.One or a plurality of Home-eNBs 72-2 are connected to one HeNBGW 74, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween through an S1 interface. TheMME unit 73 and HeNBGW 74 are equivalent to host node devices, andcontrol the connection between the user equipment (UE) 71 and each ofthe eNB 72-1 and Home-eNB 72-2 being a base station.

Further, the configuration below is currently studied in 3GPP. The X2interface between the Home-eNBs 72-2 is supported. The HeNBGW 74 appearsto the MME unit 73 as the eNB 72-1. That is, the Home-eNBs 72-2 areconnected to each other by means of the X2 interface, and controlinformation is communicated between the Home-eNBs 72-2. The HeNBGW 74appears to the MME unit 73 as the Home-eNB 72-2. The HeNBGW 74 appearsto the Home-eNB 72-2 as the MME unit 73. The interfaces between theHome-eNBs 72-2 and the MME units 73 are the same, which are the S1interfaces, in both of the case where the Home-eNB 72-2 is connected tothe MME unit 73 through the HeNBGW 74 and the case where the Home-eNB72-2 is directly connected to the MME unit 73. The HeNBGW 74 does notsupport the mobility to the Home-eNB 72-2 or the mobility from theHome-eNB 72-2 that spans the plurality of MME units 73. The Home-eNB72-2 supports a single cell.

FIG. 8 is a block diagram showing the configuration of the userequipment (user equipment 71 of FIG. 7) according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 8 is described. First, a transmission data buffer unit 803 storesthe control data from a protocol processing unit 801 and the user datafrom an application unit 802. The data stored in the transmission databuffer unit 803 is transmitted to an encoding unit 804 and is subjectedto an encoding process such as error correction. There may exist thedata output from the transmission data buffer unit 803 directly to amodulating unit 805 without the encoding process. The data encoded bythe encoding unit 804 is modulated by the modulating unit 805. Themodulated data is output to a frequency converting unit 806 after beingconverted into a baseband signal, and then is converted into a radiotransmission frequency. After that, a transmission signal is transmittedfrom an antenna 807 to the base station 72.

The user equipment 71 executes the reception process as follows. Theradio signal is received through the antenna 807 from the base station72. The received signal is converted from a radio reception frequency toa baseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data istransmitted to a decoding unit 809 and is subjected to a decodingprocess such as error correction. Among the pieces of decoded data, thecontrol data is transmitted to the protocol processing unit 801, whilethe user data is transmitted to the application unit 802. A series ofprocesses of the user equipment 71 is controlled by a control unit 810.This means that, though not shown in FIG. 8, the control unit 810 isconnected to the respective units 801 to 809.

FIG. 9 is a block diagram showing the configuration of the base station(base station 72 of FIG. 7) according to the present invention. Thetransmission process of the base station 72 shown in FIG. 9 isdescribed. An EPC communication unit 901 performs datatransmission/reception between the base station 72 and the EPCs (such asMME unit 73 and HeNBGW 74). A communication with another base stationunit 902 performs data transmission/reception to/from another basestation. The EPC communication unit 901 and the communication withanother base station unit 902 respectively transmit/receive informationto/from a protocol processing unit 903. The control data from theprotocol processing unit 903, and the user data and control data fromthe EPC communication unit 901 and the communication with another basestation unit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is transmittedto an encoding unit 905 and is then subjected to an encoding processsuch as error correction. There may exist the data output from thetransmission data buffer unit 904 directly to a modulating unit 906without the encoding process. The encoded data is modulated by themodulating unit 906. The modulated data is output to a frequencyconverting unit 907 after being converted into a baseband signal, and isthen converted into a radio transmission frequency. After that, atransmission signal is transmitted to one or a plurality of userequipments 71 through an antenna 908.

While, the reception process of the base station 72 is executed asfollows. Radio signals from one or a plurality of user equipments 71 arereceived through the antenna 908. The received signal is converted froma radio reception frequency into a baseband signal by the frequencyconverting unit 907, and is then demodulated by a demodulating unit 909.The demodulated data is transmitted to a decoding unit 910 and is thensubjected to a decoding process such as error correction. Among thepieces of decoded data, the control data is transmitted to the protocolprocessing unit 903, EPC communication unit 901, or communication withanother base station unit 902, while the user data is transmitted to theEPC communication unit 901 and the communication with another basestation unit 902. A series of processes by the base station 72 iscontrolled by a control unit 911. This means that, though not shown inFIG. 9, the control unit 911 is connected to the respective units 901 to910.

The functions of the Home-eNB 72-2 currently under discussion of 3GPPare described below (see Chapter 4.6.2 of Non-Patent Document 1). TheHome-eNB 72-2 has the same function as that of the eNB 72-1. Inaddition, the Home-eNB 72-2 has the function of discovering a suitableserving HeNBGW 74 in a case of connection to the IIeNBGW 74. TheHome-eNB 72-2 is connected only to one HeNBGW 74. That is, in a case ofthe connection to the HeNBGW 74, the Home-eNB 72-2 does not use the Flexfunction in the S1 interface. When the Home-eNB 72-2 is connected to oneHeNBGW 74, it is not simultaneously connected to another HeNBGW 74 oranother MME unit 73.

The TAC and PLMN ID of the Home-eNB 72-2 are supported by the HeNBGW 74.When the Home-eNB 72-2 is connected to the HeNBGW 74, selection of theMME unit 73 at “UE attachment” is performed by the HeNBGW 74 instead ofthe Home-eNB 72-2. The Home-eNB 72-2 may be deployed without networkplanning. In this case, the Home-eNB 72-2 is moved from one geographicalarea to another geographical area. Accordingly, the Home-eNB 72-2 inthis case is required to be connected to a different HeNBGW 74 dependingon its location.

FIG. 10 is a block diagram showing the configuration of the MMEaccording to the present invention. FIG. 10 shows the configuration ofan MME 73 a included in the MME unit 73 shown in FIG. 7 described above.A PDN GW communication unit 1001 performs data transmission/receptionbetween the MME 73 a and a PDN GW. A base station communication unit1002 performs data transmission/reception between the MME 73 a and thebase station 72 by means of the S1 interface. In the case where the datareceived from the PDN GW is user data, the user data is transmitted fromthe PDN GW communication unit 1001 to the base station communicationunit 1002 through a user plane communication unit 1003 and is thentransmitted to one or a plurality of base stations 72. In the case wherethe data received from the base station 72 is user data, the user datais transmitted from the base station communication unit 1002 to the PDNGW communication unit 1001 through the user plane communication unit1003 and is then transmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is transmitted from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data istransmitted from the base station communication unit 1002 to the controlplane control unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission/reception bymeans of the interface (IF) between the MME 73 a and the HeNBGW 74according to an information type. The control data received from theHeNBGW communication unit 1004 is transmitted from the HeNBGWcommunication unit 1004 to the control plane control unit 1005. Theprocessing results of the control plane control unit 1005 aretransmitted to the PDN GW through the PDN GW communication unit 1001.The processing results of the control plane control unit 1005 aretransmitted to one or a plurality of base stations 72 by means of the S1interface through the base station communication unit 1002, and aretransmitted to one or a plurality of HeNBGWs 74 through the HeNBGWcommunication unit 1004.

The control plane control unit 1005 includes an NAS security unit1005-1, an SAE bearer control unit 1005-2, and an idle state mobilitymanaging unit 1005-3, and performs an overall process for the controlplane. The NAS security unit 1005-1 provides, for example, security of anon-access stratum (NAS) message. The SAE bearer control unit 1005-2manages, for example, a system architecture evolution (SAE) bearer. Theidle state mobility managing unit 1005-3 performs, for example, mobilitymanagement of an idle state (LTE-IDLE state, which is merely referred toas idle as well), generation and control of paging signaling in an idlestate, addition, deletion, update, and search of a tracking area (TA) ofone or a plurality of user equipments 71 being served thereby, andtracking area list (TA list) management.

The MME 73 a begins a paging protocol by transmitting a paging messageto the cell belonging to a UE registered tracking area (TA). The idlestate mobility managing unit 1005-3 may manage the CSG of the Home-eNBs72-2 to be connected to the MME 73 a, CSG-IDs, and a whitelist.

In the CSG-ID management, the relationship between a user equipmentcorresponding to the CSG-ID and the CSG cell is managed (added, deleted,updated or searched). For example, it may be the relationship betweenone or a plurality of user equipments whose user access has beenregistered with a CSG-ID and the CSG cells belonging to this CSG-ID. Inthe whitelist management, the relationship between the user equipmentand the CSG-ID is managed (added, deleted, updated, or searched). Forexample, one or a plurality of CSG-IDs with which user registration hasbeen performed by a user equipment may be stored in the whitelist. Theabove-mentioned management related to the CSG may be performed byanother part of the MME 73 a. A series of processes by the MME 73 a iscontrolled by a control unit 1006. This means that, though not shown inFIG. 10, the control unit 1006 is connected to the respective units 1001to 1005.

The function of the MME 73 a currently under discussion of 3GPP isdescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The MME 73a performs access control for one or a plurality of user equipmentsbeing members of closed subscriber groups (CSGs). The MME 73 arecognizes the execution of paging optimization as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGW 74shown in FIG. 7 that is a HeNBGW according to the present invention. AnEPC communication unit 1101 performs data transmission/reception betweenthe HeNBGW 74 and the MME 73 a by means of the S1 interface. A basestation communication unit 1102 performs data transmission/receptionbetween the HeNBGW 74 and the Home-eNB 72-2 by means of the S1interface. A location processing unit 1103 performs the process oftransmitting, to a plurality of Home-eNBs 72-2, the registrationinformation or the like among the data transmitted from the MME 73 athrough the EPC communication unit 1101. The data processed by thelocation processing unit 1103 is transmitted to the base stationcommunication unit 1102 and is transmitted to one or a plurality ofHome-eNBs 72-2 through the S1 interface.

The data only caused to pass through (to be transparent) withoutrequiring the process by the location processing unit 1103 is passedfrom the EPC communication unit 1101 to the base station communicationunit 1102, and is transmitted to one or a plurality of Home-eNBs 72-2through the S1 interface. A series of processes by the HeNBGW 74 iscontrolled by a control unit 1104. This means that, though not shown inFIG. 11, the control unit 1104 is connected to the respective units 1101to 1103.

The function of the HeNBGW 74 currently under discussion of 3GPP isdescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW74 relays an S1 application. The HeNBGW 74 terminates the S1 applicationthat is not linked to the user equipment 71 though it is a part of theprocedures toward the Home-eNB 72-2 and towards the MME 73 a. When theHeNBGW 74 is deployed, the procedure that is not linked to the userequipment 71 is communicated between the Home-eNB 72-2 and the HeNBGW 74and between the HeNBGW 74 and the MME 73 a. The X2 interface is not setbetween the HeNBGW 74 and another node. The HeNBGW 74 recognizes theexecution of paging optimization as an option.

Next, an example of a typical cell search method in a mobilecommunication system is described. FIG. 12 is a flowchart showing anoutline from a cell search to an idle state operation performed by auser equipment (UE) in the LTE communication system. When starting thecell search, in Step ST1201, the user equipment synchronizes the slottiming and frame timing by a primary synchronization signal (P-SS) and asecondary synchronization signal (S-SS) transmitted from a neighbourbase station. Synchronization codes, which correspond to physical cellidentities (PCIs) assigned per cell one by one, are assigned to thesynchronization signals (SS) including the P-SS and S-SS. The number ofPCIs is currently studied in 504 ways, and these 504 ways are used forsynchronization, and the PCIs of the synchronized cells are detected(specified).

Next, in Step ST1202, the user equipment detects a reference signal RS(cell-specific reference signal (CRS)) transmitted from the base stationper cell and measures the received power (also referred to as RSRP). Thecode corresponding to the PCI one by one is used for the referencesignal RS, and separation from another cell is enabled by correlationusing the code. The code for RS of the cell is derived from the PCIspecified in Step ST1201, which makes it possible to detect the RS andmeasure the RS received power.

Next, in Step ST1203, the user equipment selects the cell having thebest RS reception quality (for example, cell having the highest RSreceived power, that is, best cell) from one or more cells that havebeen detected up to Step ST1202.

In Step ST1204, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas transmission bandwidth configuration (dl-bandwidth)), transmissionantenna number, and system frame number (SFN).

In Step ST1205, next, the user equipment receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information related to the access to thecell, information related to cell selection, and scheduling informationof other SIB (SIBk; k is an integer equal to or larger than two). Inaddition, the SIB1 contains a tracking area code (TAC).

In Step ST1206, next, the user equipment compares the TAC of the SIB1received in Step ST1205 with the TAC in the tracking area (TA) list thathas been already possessed by the user equipment. In a case where theTAC received in Step ST1205 is identical to the TAC included in the TAlist as a result of the comparison, the user equipment enters an idlestate operation in the cell. In a case where the TAC received in StepST1205 is not included in the TA list as a result of the comparison, theuser equipment requires a core network (EPC) (including MME and thelike) to change a TA through the cell for performing tracking areaupdate (TAU). The core network updates the TA list based on anidentification number (such as a UE-ID) of the user equipmenttransmitted from the user equipment together with a TAU request signal.The core network transmits the updated TA list to the user equipment.The user equipment rewrites (updates) the TAC list of the user equipmentwith the received TA list. After that, the user equipment enters theidle state operation in the cell.

As to the LTE, LTE-A, and universal mobile telecommunication system(UMTS), the introduction of a closed subscriber group (CSG) cell isstudied. As described above, access is allowed for only one or aplurality of user equipments registered with the CSG cell. A CSG celland one or a plurality of user equipments registered with the CSG cellconstitute one CSG. A specific identification number referred to asCSG-ID is added to the thus constituted CSG. Note that one CSG maycontain a plurality of CSG cells. After being registered with any one ofthe CSG cells, the user equipment can access another CSG cell of the CSGto which the registered CSG cell belongs.

Alternatively, the Home-eNB in the LTE and LTE-A or the Home-NB in theUMTS is used as the CSG cell in some cases. The user equipmentregistered with the CSG cell has a whitelist. Specifically, thewhitelist is stored in the subscriber identity module (SIM)/USIM. TheCSG information of the CSG cell with which the user equipment has beenregistered is stored in the whitelist. Specific examples of the CSGinformation include CSG-ID, tracking area identity (TAI) and TAC. Anyone of the CSG-ID and TAC is adequate as long as they are associatedwith each other. Alternatively, GCI is adequate as long as the CSG-IDand TAC are associated with global cell identity (GCI).

As can be seen from the above, the user equipment that does not have awhitelist (including a case where the whitelist is empty in the presentinvention) is not allowed to access the CSG cell but is allowed toaccess the non-CSG cell only. On the other hand, the user equipmentwhich has a whitelist is allowed to access the CSG cell of the CSG-IDwith which registration has been performed as well as the non-CSG cell.

Splitting of all physical cell identities (PCIs) into ones reserved forCSG cells and the others reserved for non-CSG cells is discussed in 3GPP(see Non-Patent Document 1). There is a range of PCIs in all the PCIs,which is reserved by the network for use by CSG cells (see Chapter10.5.1.1 of Non-Patent Document 1). Splitting the range of PCIs isreferred to PCI-split as times. The PCI split information is broadcastin the system information from the base station to the user equipmentsbeing served thereby. Non-Patent Document 5 discloses the basicoperation of a user equipment by PCI split. The user equipment that doesnot have the PCI split information needs to perform cell search usingall the PCIs (for example, using all 504 codes). On the other hand, theuser equipment that has the PCI split information is capable ofperforming cell search using the PCI split information.

Further, it has been determined that the PCIs for hybrid cells are notcontained in the PCI range for CSG cells in 3GPP (see Chapter 10.7 ofNon-Patent Document 1).

According to 3GPP, there are two modes in the method of selecting orreselecting a CSG cell by a user equipment. One is an automatic mode.The feature of the automatic mode is described below. The user equipmentperforms selection or reselection with the use of an allowed CSG list(allowed CSG ID list) in the user equipment. After the completion ofPLMN selection, the user equipment camps on one cell in the selectedPLMN only in a case of a non-CSG cell or a CSG cell with a CSG IDpresent in the allowed CSG list. The user equipment disables anautonomous search function of the CSG cell if the allowed CSG list ofthe user equipment is empty (see Chapter 5.2.4.8.1 of Non-PatentDocument 3).

The second is a manual mode. The feature of the manual mode is describedbelow. The user equipment shows a list of available CSGs in thecurrently selected PLMN to a user. The list of CSGs provided to the userby the user equipment is not limited to the CSGs included in the allowedCSG list stored in the user equipment. The user selects the CSG based onthe list of CSGs, and then the user equipment camps on the cell with theselected CSG ID, to thereby attempt registration (see Non-PatentDocument 3).

The HeNB and HNB are required to support various services. For example,an operator causes a predetermined HeNB and HNB to register userequipments therein and permits only the registered user equipments toaccess the cells of the HeNB and HNB, which increases radio resourcesavailable for the user equipments and enables high-speed communication.In such a service, the operator correspondingly sets a higher chargecompared with a normal service.

In order to achieve the above-mentioned service, the closed subscribergroup cell (CSG cell) accessible only to the registered (subscribed ormember) user equipments is introduced. It is required to install a largenumber of closed subscriber group cells (CSG cells) in shopping malls,apartment buildings, schools, companies and the like. For example, thefollowing manner of use is required; the CSG cells are installed foreach store in shopping malls, for each room in apartment buildings, foreach classroom in schools, and for each section in companies such thatonly the users who have registered with the respective CSG cells arepermitted to use those CSG cells. The HeNB/HNB is required not only tocomplement the communication outside the coverage of the macro cell(area complementing HeNB/HNB) but also to support various services asdescribed above (service providing HeNB/HNB). This also leads to a casewhere the HeNB/HNB is installed within the coverage of the macro cell.

As described above, CA is studied in the LTE-A system, in which two ormore CCs are aggregated to support transmission bandwidths up to 100MHz, which are wider than the frequency bandwidths of the LTE system.

FIG. 13 is a diagram showing the concept of CA. An eNB shown in FIG. 13configures a cell n configured by a DL CCn and a UL CCn which isassociated with the DL-CCn by a DL/UL link via SIB2. The carrierfrequency of the DL CCn is denoted by Fn (DL), and the carrier frequencyof the UL CCn is denoted by Fn (UL). Here, n is an integer of one tofive.

A UE camps on the cell1 and performs RRC connection indicated by anarrow 1301. As a result, the cell1 becomes a PCell.

After that, the eNB notifies the UE of the information related to theCCs to be aggregated through dedicated RRC signaling indicated by anarrow 1302. The information related to a cell m configured by a DL CCmand a UL CCm, for example, system information is notified as theinformation related to the CCs. Here, m is an integer of two to five.The eNB notifies the UE of the information related to the CCs in thismanner, whereby the cell2 to the cell5 become SCells.

As described above, the eNB performs CA for the UE with the cell1 to thecell5. Then, the UE performs communication with the cell1 to the cell5based on CA, as indicated by an arrow 1303.

A configuration example of a UE that supports CA is described. Itsuffices that in the configuration shown in FIG. 8 described above, apart or the whole of the modulating unit 805, frequency converting unit806, antenna 807, and demodulating unit 808 is caused to support a widerbandwidth. In the transmitter, a part or the whole of the modulatingunit 805, frequency converting unit 806, and antenna 807 may be causedto operate in a band including a predetermined number of contiguous ULCCs. In the receiver, a part or the whole of the antenna 807, frequencyconverting unit 806, and demodulating unit 808 may be caused to operatein a band including a predetermined number of contiguous DL CCs. Thisenables to support CA by a predetermined number of contiguous UL CCs orDL CCs.

As another method, it suffices that a plurality of a part or the wholeof the modulating unit 805, frequency converting unit 806, antenna 807,and demodulating unit 808 are provided in parallel to operate in a bandincluding a predetermined number of non-contiguous UL CCs or DL CCs. Inthe transmitter, a plurality of a part or the whole of the modulatingunit 805, frequency converting unit 806, and antenna 807 may be providedin parallel so as to operate in a band including a predetermined numberof non-contiguous UL CCs. In the receiver, a plurality of a part or thewhole of the antenna 807, frequency converting unit 806, anddemodulating unit 808 may be provided in parallel so as to operate in aband including a predetermined number of non-contiguous DL CCs. Thisenables to support CA with a predetermined number of non-contiguous ULCCs or DL CCs. Alternatively, the two configurations described above maybe appropriately combined.

A configuration example of an eNB that supports CA is described. Itsuffices that in the configuration shown in FIG. 9 described above, theprotocol processing unit 903 performs the process for a UE for which CAis performed per cell configured by an eNB, and the transmission databuffer unit 904, encoding unit 905, modulating unit 906, frequencyconverting unit 907, antenna 908, demodulating unit 909, and decodingunit 910 are configured per cell. This enables to perform CA for a UE bycells configured by an eNB.

A problem to be solved in the first embodiment is described below.Non-Patent Document 10 discloses that a CSG indication and a CSG-ID canbe configured per cell (CC). However, Non-Patent Document 10 does notdescribe the method of notifying user equipments of the configurationcontent. As a result, the operation of the communication system cannotbe determined uniquely, leading to a problem that services cannot beprovided appropriately.

A solution in the first embodiment is described below. Each cell (CC)notifies user equipments being served thereby of the CSG indication andCSG-ID configured per cell (CC). The CSG indication and CSG-ID of theSCell are notified user equipments during a call, that is, inRRC_CONNECTED, by “RRC Connection Reconfiguration message” of dedicatedRRC signaling from the PCell.

The first embodiment described above can achieve the following effects.The method of notifying user equipments of the CSG indication and CSG-IDconfigured per cell (CC) is determined uniquely, which enables to stablyprovide services. The first embodiment can improve a data rate usingstable carrier aggregation.

Second Embodiment

A problem to be solved in a second embodiment is described below. In acase where the first embodiment is used, the following problem occurs.As described above, in access from a user equipment through a CSG cell,an MME performs access control, that is, restricts access from a UE to aCSG cell. That is, a base station does not restrict access to the CSG.As a result, for a UE unregistered with the CSG to which a cell belongs,the cell (CC) may be configured as a SCell to become active.

Therefore, in a communication system, the following problem occurs if anMME performs access control in access from a user equipment through aCSG cell. Considered here is a case in which a base station configures,for a user equipment unregistered with a CSG to which a cell belongs,the cell as a SCell. In this case, after the cell is configured as aSCell, access from the user equipment through the cell is not permittedthrough access control by the MME. In such a case, carrier aggregationcannot be performed. In a case where a cell belonging to the CSG isprovided by a base station as described above, a problem that a datarate cannot be improved using carrier aggregation arises.

In a case where a base station configures, for a user equipmentunregistered with a CSG to which a cell belongs, the cell as a SCell,the following problem occurs in the user equipment. It is uncertainwhether the user equipment performs communication through the cell (CC)in accordance with the SCell addition or modification to be notifiedfrom a PCell or judges that it cannot access the cell (CC) by CSG accessrestriction based on a whitelist stored in a USIM of the user equipment.This leads to a problem that an operation of a user equipment becomesunstable. Accordingly, an operation of a communication system cannot bedetermined uniquely, leading to a problem that services cannot beprovided appropriately.

A solution in the second embodiment is described below. In a case ofconfiguring a cell as a SCell, the communication system can providenormal services to user equipments through the cell. In a case where theSCell is configured, the user equipment judges to be able to receivenormal services through the cell.

In a case of configuring a cell as a SCell, even when the cell (SCell)belongs to a CSG and the user equipment is unregistered with the CSG,the communication system may provide normal services to the userequipment through the cell. In a case where a cell is configured as aSCell, the user equipment may judge to be able to receive normalservices through the cell even if it has been unregistered with the CSGto which the cell (SCell) belongs.

The following two (1) and (2) are disclosed as specific examples of thecase of configuring a cell as a SCell.

(1) The configuration content as a Scell is notified to a userequipment. Specific examples of the configuration content include aCSG-ID and a CSG indication per CC.

(2) The configuration content as a Scell is not notified to a userequipment. Specific examples of the configuration content include aCSG-ID and a CSG indication per CC. The following two (a1) and (a2) aredisclosed as specific examples of the case where a cell does not notifythe user equipment of the configuration content. (a1) Case where anotification of the configuration content is omitted. Specific examplesof the configuration content include a CSG-ID and a CSG indication perCC. (a2) Case where a SCell does not belong to a CSG. That is, a casewhere a SCell is not a CSG cell.

The following two (1) and (2) are disclosed as specific examples of thecase where a cell is configured as a SCell.

(1) The configuration content as a Scell is received. Specific examplesof the configuration content include a CSG-ID and a CSG indication perCC.

(2) The configuration content as a Scell is not received.

The solution in the second embodiment described above is performed,whereby a data rate using carrier aggregation can be improved even in acase where a cell belonging to a CSG is provided by a base station.Also, the operation of a user equipment can be determined uniquely,which enables to appropriately provide services.

A specific example of the operation of an MME is disclosed below. TheMME does not perform access control for a user equipment through a cellconfigured as a SCell by a base station. The MME may not perform accesscontrol for a user equipment through a CSG cell configured as a SCell bya base station. The MME may only perform access control for a userequipment through a PCell. The MME may only perform access control for auser equipment through a PCell belonging to the CSG. The MME may onlyperform access control for a user equipment through a PCell being a CSGcell.

The following two (1) and (2) are disclosed as specific examples of theoperation of the base station.

(1) In a case of performing carrier aggregation, a base station canconfigure any cell of the base station as a SCell. Alternatively, in acase of performing carrier aggregation, the base station may enable toconfigure any cell as a SCell even if a cell belonging to the CSG isprovided by the base station.

(2) In a case of performing carrier aggregation, the base station canrender any cell provided by the base station active as a SCell.Alternatively, in a case of performing carrier aggregation, the basestation may render any cell active as a SCell even if a cell belongingto the CSG is provided by in the base station.

A specific example of the operation of the user equipment is disclosedbelow. A user equipment does not perform CSG access restriction on acell notified of the configuration content as a SCell (hereinafter,merely referred to as “SCell” in some cases). The following three (1) to(3) are disclosed as specific examples of the method in which a userequipment does not perform CSG access restriction.

(1) Even in a case where the configuration content as a SCell contains aCSG-indication and a CSG-ID of the SCell, a user equipment does notperform access restriction using the CSG-indication and CSG-ID. Forexample, a user equipment does not compare the CSG-ID of the SCellcontained in the configuration content as a SCell and the CSG-ID in theUSIM of the user equipment. Alternatively, even in a case where theCSG-ID of the SCell contained in the configuration content as a SCelldoes not match the CSG-ID contained in the USIM of the user equipment,the user equipment may not perform judgment that access is not allowed.Still alternatively, a user equipment may not notify the CSG-indicationand CSG-ID of the SCell by the configuration as a SCell.

(2) A user equipment does not perform access restriction using theCSG-indication and CSG-ID that are broadcast from a cell configured as aSCell using the broadcast information. For example, a user equipmentdoes not compare the CSG-ID broadcast from the cell configured as aSCell using the broadcast information and the CSG-ID in the USIM of theuser equipment. Alternatively, even in a case where the CSG-ID broadcastfrom the cell configured as a SCell using the broadcast information doesnot match the CSG-ID contained in the USIM of the user equipment, theuser equipment may not perform such judgment that access is not allowed.Alternatively, a user equipment may not receive or may ignore the CSG-IDbroadcast from a cell configured as a SCell using the broadcastinformation. Alternatively, a user equipment may not receive or mayignore the SIB1 broadcast from the cell configured as a SCell.Alternatively, a user equipment may not receive or may ignore the SIBbroadcast from a cell configured as a SCell. Alternatively, a userequipment may not receive or may ignore the broadcast informationbroadcast from a cell configured as a SCell.

(3) Combination of (1) and (2) above.

As to a CSG cell, the deployment in which services are preferentiallyprovided to CSG members belonging to the same CSG is studied asdescribed above. Specific examples of the preferential treatmentprobably include the preferential allocation of resources to CSG membersand the discount of communication costs for CSG members. It isconceivable that along with the above, the charging setting may differbetween CSG members and non-CSG members.

Specific examples of the charging setting in a case where the secondembodiment is used are described below. A core network side isconceivable as a specific example of the judging entity. The followingtwo (1) and (2) are disclosed as specific examples of the entity on thecore network side; (1) MME and (2) home subscriber server (HSS).

The following three (1) to (3) are disclosed as specific examples of thecharging setting. (1) Charging for use of SCells unregistered with a CSGis set to be similar to charging of the members registered with the CSG.(2) Charging for use of SCells unregistered with a CSG is set to besimilar to charging of the members unregistered with the CSG. (3)Charging for use of SCells unregistered with a CSG is set to be similarto that in a case of PCells.

The following three (1) to (3) are disclosed as specific examples ofhandling services. (1) The use of SCells unregistered with a CSG ishandled similarly to that of services for members registered with theCSG. (2) The use of SCells unregistered with a CSG is handled similarlyto that of services for members unregistered with the CSG. (3) The useof SCells unregistered with a CSG is handled as in the case of PCell.

Next, a specific example of a sequence of a communication system in thesecond embodiment is described with reference to FIG. 14. FIG. 14 is adiagram showing an example of the sequence of the communication systemin the second embodiment. This operation example describes a case inwhich a base station A providing a plurality of cells (CCs) including acell and a cell2 is present, where a UE selects the cell of the basestation A as the best cell and camps on the cell to start communication,and thereafter, the cell2 is configured as a SCell. The plurality ofcells of the base station A are formed of component carriers havingdifferent frequencies. The base station A aggregates two or more cellsamong a plurality of cells, that is, performs carrier aggregation (CA)and transmits/receives component carriers of the aggregated cells inparallel to perform radio communication with UEs.

In Step ST1401, the UE selects a cell having the best RS receptionquality, for example, the best cell having the highest RS receptionpower. In this operation example, in Step ST1401, the UE selects thecell1 of the base station A as the best cell. When selecting the bestcell in Step ST1401, the UE moves to Step ST1402.

In Step ST1402, the UE receives the MIB of the best cell selected inStep ST1401. Specifically, the UE receives the PBCH of the best cellselected in Step ST1401 and obtains a BCCH being the broadcastinformation. The MIB containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas transmission bandwidth configuration (dl-bandwidth)), transmissionantenna number, and system frame number (SFN).

In Step ST1403, the base station A notifies the UE of the SIB. The SIB1of the SIB contains the information related to access to the cell, forexample, CSG identity (CSG-ID), CSG indication, information related tocell selection, and scheduling information of other SIB (SIBk; k is aninteger equal to or larger than two).

Specifically, in a case where the cell operates in an open access modeor hybrid access mode, the CSG indication is set to “FALSE”, which isbroadcast from the cell. Meanwhile, in a case where the cell operates ina closed access mode, the CSG indication is set to “TRUE”, which isbroadcast from the cell. In the case where the CSG indication is set to“TRUE”, the user equipment can access the cell only in a case where theCSG identity (CSG-ID) matches the CSG identity (CSG-ID) in the whiteliststored in, for example, the USIM of the user equipment (see Non-PatentDocument 2).

In this operation example, the cell broadcasts “CSG-indication_cell” tothe UE as a CSG indication and broadcasts “CSG-ID_cell” to the UE as aCSG identity.

In Step ST1404, the UE receives the SIB. Specifically, based on the cellconfiguration information of the MIB, the UE receives the DL-SCH of thecell and obtains the SIB1 in the broadcast information BCCH. The UEreceives other SIB based on the scheduling information of the other SIBin the SIB1. When receiving the SIB in Step ST1404 in this manner, theUE moves to Step ST1405.

In Step ST1405, the UE judges whether or not the CSG indication(CSG-indication) in the SIB received in Step ST1404 is “TRUE”. In otherwords, the UE judges whether or not the access mode of the SCell is aclosed access mode. In a case of judging that the CSG indication is“TRUE” in Step ST1405, the UE moves to Step ST1406. In a case of judgingthat the CSG indication is not “TRUE”, that is, is “FALSE” in StepST1405, the UE moves to Step ST1407.

In Step ST1406, the UE judges whether or not the own UE has beenregistered with the CSG indicated by the CSG identity in the SIBreceived in Step ST1404. The UE may judge whether or not the CSGidentity in the SIB received in Step ST1404 matches the CSG identity inthe whitelist stored in, for example, the USIM of the UE.

In a case of judging that the own UE has been registered in Step ST1406,the UE moves to Step ST1407. Alternatively, in a case of judging thatthe CSG identity in the received SIB matches the CSG identity in thewhitelist stored in, for example, the USIM of the UE in Step ST1406, theUE may move to Step ST1407.

In a case of judging that the own UE has been unregistered in StepST1406, the UE returns to Step ST1401 to select another cell as the bestcell. Alternatively, in a case of judging that the CSG identity in thereceived SIB does not match the CSG identity in the whitelist stored in,for example, the USIM of the UE in Step ST1406, the UE may return toStep ST1401 to select another cell as the best cell.

In Step ST1407, the UE camps on the cell selected in Step ST1401. Inthis operation example, the UE camps on the cell of the base station A.

In Step ST1408, the UE performs RRC connection with the cell to whichthe UE has camped on in Step ST1407. In a base station by which carrieraggregation can be performed, the cell with which RRC connection hasbeen performed is referred to as PCell. The PCell corresponds to aconnected cell. In this operation example, the UE performs RRCconnection with the cell of the base station A.

In Step ST1409, the UE notifies the MME of the initial NAS via the cellwith which RRC connection has been performed. In this operation example,the UE notifies the MME of the initial NAS message via the cell of thebase station A.

In Step ST1410, the cell1 notifies the MME of the NAS message receivedfrom the UE in Step ST1409. As a specific example of the method ofnotifying the NAS message, the cell maps the NAS message received fromthe UE to “INITIAL UE MESSAGE” and notifies the MME of the NAS message.This notification includes the CSG identity and cell access mode of thebase station (cell), in addition to the NAS message received from the UEin Step ST1409 (see TS 36.413 V9.5.0 (hereinafter, referred to as“Non-Patent Document 11”) by 3GPP). In this operation example, the cellnotifies the MME of the CSG-ID_cell and Cell Access Mode_cell1 as theCSG identity and cell access mode, respectively.

In Step ST1411, the MME judges whether or not the cell access modereceived in Step ST1410 is “closed access mode”. In a case of judgingthat the cell access mode is “closed access mode” in Step ST1411, theMME moves to Step ST1412. In a case of judging that the cell access modeis not “closed access mode”, that is, is “open access mode” or “hybridaccess mode” in Step ST1411, the MME moves to Step ST1413.

In Step ST1412, the MME judges whether or not the UE has been registeredwith the CSG identity received in Step ST1410. In a case of judging thatthe UE has been registered in Step ST1412, the MME moves to Step ST1413.In a case of judging that the UE has not been registered, that is, hasbeen unregistered in Step ST1412, the MME moves to Step ST1414. In acase of judging whether or not the UE has been registered in StepST1412, the MME may inquire the HSS or use the information stored in theHSS.

In Step ST1413, the MME judges that communication with the UE via thecell that has notified the NAS message from the UE in Step ST1410 ispossible. In this operation example, the MME judges that communicationwith the UE via the cell1 of the base station A is possible.

In Step ST1414, the MIME judges that communication with this UE via thecell that has notified the NAS message from the UE in Step ST1410 is notpossible.

In Step ST1415, the MME notifies the UE that has notified the NASmessage via a cell in Step ST1409 of the judgment results as to whetheror not communication with the UE via the cell is possible. In thisoperation example, the MME notifies the UE of the judgment results thatcommunication with the UE via the cell is possible.

In Step ST1416, the UE judges whether or not communication via the cellis possible based on the judgment results received in Step ST1415. In acase of judging that communication is possible in Step ST1416, the UEmoves to Step ST1417. In a case of judging that communication is notpossible in Step ST1416, the UE ends the process and moves to otherprocess. The other process is not specific to the present invention,which is not described here. In this operation example, the UE judgesthat communication via the cell is possible.

In Step ST1417, the cell starts communication with the UE. In thisoperation example, the cell1 starts communication with the UE as aPCell.

In Step ST1418, the cell determines to configure another cell as aSCell. The SCell corresponds to an aggregable cell and can be aggregatedwith the PCell. In this operation example, the cell serving as a PCelldetermines to configure the cell2 as a SCell. In the present embodiment,CSG access restriction is not performed in determining a SCell.Specifically, the processes corresponding to Steps ST1410 to ST1415 arenot performed in the determination of a SCell in Step ST1418.

In Step ST1419, the cell notifies, using dedicated RRC signaling, the UEof a SCell to be added or a SCell to be modified and the configurationcontent of the cell. In this operation example, the cell2 as a SCell tobe added and the configuration content of the cell2 are notified using“RRC Connection Reconfiguration message” of dedicated RRC signaling. Onthat occasion, the system information of the cell2 is notified as well.

In the present embodiment, when a SCell is added or modified, the UEdoes not perform CSG access restriction on the SCell. Specifically, theUE does not perform the processes corresponding to Steps ST1405 andST1406 using the configuration content of the cell2 received in StepST1419 or the system information of the cell2 received in Step ST1419.

In Step ST1420, the cell2 broadcasts the SIB to UEs being servedthereby. Specifically, the information related to access to the cell2 isbroadcast. For example, “CSG-ID_cell2” or the like and“CSG-indication_cell2” or the like are broadcast as the CSG identity andthe CSG indication, respectively. In the present embodiment, when aSCell is added or modified, the UE does not perform CSG accessrestriction on the SCell. Specifically, the UE does not perform theprocesses corresponding to Steps ST1405 and ST1406 using the systeminformation of the cell2 broadcast from the cell2 in Step ST1420.Alternatively, the UE may not receive the system information of thecell2 broadcast from the cell2 in Step ST1420.

In Step ST1421, the UE notifies the cell being a PCell that theconfiguration of a SCell to be added or SCell to be modified has beenfinished, which had been received in Step ST1419. This is notifiedusing, for example, “RRC Connection Reconfiguration Complete”. In thisoperation example, the UE notifies the cell being a PCell that theconfiguration of a SCell has been finished.

In Step ST1422, the cell being a SCell starts communication with the UE.In this operation example, the cell2 starts communication with the UE asa SCell.

The second embodiment described above can achieve the following effects.The operation as a communication system can be stabilized whileimproving a data rate using carrier aggregation, which enables toappropriately provide services.

The present embodiment can be used in combination with the firstembodiment described above.

First Modification of Second Embodiment

The present modification describes a point to be further improved in thesecond embodiment described above. The present modification mainlydescribes a portion different from the solution in the second embodimentdescribed above, and a portion not to be described is similar to thesecond embodiment.

Each cell (CC) can be configured whether or not it can be used as aSCell. This configuration may be also referred to as “SCell useconfiguration”. The PCell determines to configure a cell as a SCell inaccordance with “SCell use configuration” of each cell. The PCelldetermines to configure, as a SCell, a cell indicating that it can beused in “SCell use configuration”. The PCell does not configure a cellindicating that it cannot be used as a SCell in “SCell useconfiguration”.

The following three (1) to (3) are disclosed as specific examples of theSCell use configuration. (1) Whether or not a cell can be used. (2)Indication that a cell can be used, where an effect of a smaller amountof information compared with the specific example (1) can be achieved.(3) Indication that a cell cannot be used, where an effect of a smalleramount of information compared with the specific example (1) can beachieved.

The following three (1) to (3) are disclosed as specific examples of themethod in which a PCell knows “SCell use configuration” of another cell.

(1) Before determining to configure a cell as a SCell, the PCell selectsa SCell candidate cell. The PCell inquires the SCell candidate cellabout “SCell use configuration” of the SCell candidate cell.Alternatively, a base station or a control unit of the base station maydetermine “SCell use configuration” of each cell.

(2) Each cell notifies the control unit of the base station of “SCelluse configuration” of the own cell. Before determining to configure acell as a SCell, the PCell selects a SCell candidate cell. The PCellinquires the control unit of the base station about “SCell useconfiguration” of the SCell candidate cell. Before the inquiry from thePCell, the control unit of the base station may notify each cell (PCell)of “SCell use configuration” of each cell. Alternatively, the basestation or the control unit of the base station may determine “SCell useconfiguration” of each cell.

(3) Each cell notifies another cell of “SCell use configuration” of theown cell. Alternatively, the base station or the control unit of thebase station may determine “SCell use configuration” of each cell.

The PCell may select a SCell candidate cell set including one or aplurality of cells before determining to configure a cell as a SCell. Itsuffices that the SCell candidate cell set is configured based on, forexample, UE capability. As a specific example of the configurationmethod based on UE capability, a PCell selects a SCell candidate cell ora SCell candidate cell included in the SCell candidate cell set from thecells belonging to a frequency band at which a UE is allowedtransmission and reception. This leads to an effect that a control delaywhen a SCell is determined can be prevented. It suffices that a SCellcandidate cell is selected from a SCell candidate cell set.

“SCell use configuration” may be changed. “SCell use configuration” canbe changed, which leads to an effect that cells can be operatedflexibly.

“SCell use configuration” may be changed based on the conditions of“SCell use configuration”. The following six (1) to (6) are disclosed asspecific examples of the conditions of “SCell use configuration”. (1)Load state of the cell. For example, in a case where load is high orthere are a large number of user equipments being served by a cell,“SCell use configuration” is set to “cannot be used”, whereby the cellcan reserve radio resources for user equipments being served thereby.(2) Access mode of the cell. Specific examples of the access modeinclude an open access mode, a closed access mode, and a hybrid accessmode. (3) Transmission power of the cell. (4) Coverage of the cell. (5)Power-on state or low-consumption-power operation state of the cell. (6)Combination of (1) to (5) above.

The following five (1) to (5) are disclosed as specific examples of thetiming at which “SCell use configuration” is notified.

(1) Periodically. This enables to support a change of “SCell useconfiguration”.

(2) At the time of change. This enables to support a change of “SCelluse configuration”, similarly to the specific example (1). Also, aneffect that the number of notification times is reduced compared withthe specific example (1) can be achieved.

(3) At the time when a base station is installed. This achieves aneffect that control is made more easily compared with the specificexample (1).

(4) At the time when an operation of each cell is started. This canachieve an effect that control is made more easily compared with thespecific example (1). Also, an effect that a more flexible operation canbe made per cell compared with the specific example (3) can be achieved.

(5) At the time of power-on of each cell. This can achieve an effectthat control is made more easily compared with the specific example (1).Also, an effect that a more flexible operation can be made per cellcompared with the specific example (3) can be achieved.

Next, a specific example of a sequence of a communication system in thefirst modification of the second embodiment is described with referenceto FIG. 15. FIG. 15 is a diagram showing an example of the sequence ofthe communication system in the first modification of the secondembodiment. The processes of Steps ST1401 to ST1416 of FIG. 14 in thefirst modification of the second embodiment are similar to those of thesecond embodiment, which are not illustrated and described here.Illustration and description are given from the process of Step ST1417of FIG. 14. The sequence shown in FIG. 15 is similar to the sequenceshown in FIG. 14, where the same steps are denoted by the same stepnumbers and common description is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where a UE selects the cell1 of the base station A as the bestcell and camps on the cell to start communication, and thereafter, thecell2 is configured as a SCell. A case in which each cell notifies thecontrol unit of the base station of “SCell use configuration” of the owncell is disclosed as a specific example of the method in which a PCellknows “SCell use configuration” of another cell. The case of the timewhen a base station is installed is disclosed as a specific example ofthe timing at which “SCell use configuration” is notified.

In Step ST1501, a base station is installed. In this operation example,the base station A providing a plurality of cells (CCs) including thecell and cell2 is installed.

In Steps ST1502 and ST1503, each cell of the base station notifies acontrol unit of the base station of the configuration of the own cell.The configuration of the own cell includes “SCell use configuration”. Inthis operation example, in Step ST1502, the cell1 notifies the controlunit of “SCell use configuration” of the cell1 being the own cell. InStep ST1503, the cell2 notifies the control unit of “SCell useconfiguration” of the cell2 being the own cell.

Then, the processes of Steps ST1401 to ST1407 shown in FIG. 14 describedabove are performed, so that the UE selects the cell of the base stationA as the best cell and camps on the cell1. Then, the processes of StepsST1408 to ST1416 shown in FIG. 14 described above are performed, andthen, the process moves to Step ST1417.

In Step ST1417, a cell being a PCell starts communication with the UE.In this operation example, the cell1 starts communication with the UE asa PCell.

In Step ST1504, the cell being a PCell selects another cell as a SCellcandidate. In this operation example, the cell serving as a PCellselects the cell2 as a SCell candidate.

In Step ST1505, the cell being a PCell inquires the control unit aboutthe configuration of a cell being a SCell candidate selected in StepST1504. The cell being a PCell may inquire the control unit about “SCelluse configuration” of the SCell candidate. In this operation example,the cell1 being a PCell inquires the control unit about “SCell useconfiguration” of the cell2 selected as a SCell candidate.

In Step ST1506, the control unit responds to the inquiry from the cellbeing a PCell in Step ST1505. The control unit may notify the cell beinga PCell of “SCell use configuration” of an inquiry target cell. In thisoperation example, the control unit notifies the cell being a PCell of“use is allowed” being “SCell use configuration” of the cell2 being aninquiry target cell.

In Step ST1507, the cell being a PCell judges whether or not the cellbeing a SCell candidate selected in Step ST1504 can be used as a SCell.In this judgment, the response results to the inquiry, which have beenreceived from the control unit in Step ST1506, are used.

In a case of judging that the cell being a SCell candidate selected inStep ST1504 can be used as a SCell in Step ST1507, the cell being aPCell moves to Step ST1508. In a case of judging that the cell being aSCell candidate selected in Step ST1504 cannot be used as a SCell inStep ST1507, the cell being a PCell returns to Step ST1504 to selectanother cell as a SCell candidate.

In this operation example, the cell being a PCell judges that the cell2being a SCell candidate can be used as a SCell, and then moves to StepST1508.

In Step ST1508, the cell being a PCell determines to configure the cellbeing a SCell candidate as a SCell. In this operation example, the cellbeing a PCell determines to configure the cell2 being a SCell candidateas a SCell. In this modification, CSG access restriction is notperformed in determination of a SCell, as in the second embodiment.Specifically, in the determination of a SCell in Step ST1508, theprocesses corresponding to Steps ST1410 to ST1415 shown in FIG. 14described above are not performed.

The first modification of the second embodiment described above canachieve the following effects in addition to the effects of the secondembodiment. Whether or not a cell can be used as a SCell can beconfigured on a cell basis of the base station. This enables toconfigure whether or not a radio resource is occupied for userequipments that use the cell as a Pcell on a cell basis. Therefore,cells can be operated with more precision.

The present modification can be used in combination with the firstembodiment described above.

Third Embodiment

A problem to be solved in a third embodiment is described below. In acase where the second embodiment described above is used, the followingproblem occurs. A CSG is a cell for specific subscribers, in whichsubscribers who are allowed to use can be specified by an operator. Thisleads to a problem that the second embodiment in which the userequipment unregistered with the CSG to which a cell belongs uses aresource of the cell contradicts the gist of the CSG.

As to the CSG cell, such an operation that CSG members belonging to thesame CSG are preferentially provided with services is studied. Specificexamples of the preferential treatment include the preferentialallocation of resources to CSG members and discount of communicationcosts for CSG members. Along with this, the charging setting may differbetween the CSG members and non-CSG members.

In a case where the second embodiment is used, if the user which belongsto a CSG wishes to receive some services or apply for charging setting,the user will end up in using CCs unregistered with the CSG by thesetting from the PCell irrespective of his/her wish. This causes aproblem that a user-friendly communication system cannot be constructed.

A solution in the third embodiment is described below. The presentembodiment describes a portion different from the solution in the secondembodiment described above, and a portion not to be described is similarto the second embodiment.

The base station can configure a cell (CC) belonging to the same CSG asthat of a PCell as a SCell. The base station may render a cell (CC)belonging to the same CSG as that of a PCell active as a SCell.Alternatively, in a case where a PCell belongs to the CSG, the basestation can configure a cell (CC) belonging to the same CSG as that ofthe PCell as a SCell. In a case where a PCell belongs to the CSG, thebase station may render a cell (CC) belonging to the same CSG as that ofa PCell active as a SCell. Still alternatively, in a case where a PCelldoes not belong to the CSG, the base station can configure the cell (CC)that does not belong to the CSG as a SCell. In a case where a PCell doesnot belong to the CSG, the base station may render a cell (CC) that doesnot belong to the CSG active as a SCell.

Also in the third embodiment, as to the PCell, CSG access restriction ina user equipment and an MME are performed, as in the second embodiment.Therefore, the use of the solution in the present embodiment enables toprevent a user equipment unregistered with a CSG to which a cell belongsfrom using a resource of the cell as a SCell.

A specific example of the operation of the MME is disclosed below. TheMME omits access control for a user equipment via a cell configured as aSCell by the base station, as in the case of the access control for auser equipment via a PCell. The MME may only perform access control fora user equipment via a PCell. The MME may only perform access controlfor a user equipment via a PCell belonging to the CSG. The MME may onlyperform access control for a user equipment via a PCell being a CSGcell.

The following three (1) to (3) are disclosed as specific examples of themethod in which a PCell knows whether or not another cell belongs to aCSG or knows a CSG-ID to which another cell belongs.

(1) Before determining to configure a cell as a SCell, the PCell selectsa SCell candidate cell. The PCell inquires the SCell candidate cellabout whether or not the SCell candidate cell belongs to a CSG and abouta CSG-ID to which the SCell candidate cell belongs.

The PCell may inquire about “CSG indication” and “CSG-ID” in place ofinquiring about “whether or not belonging to the CSG” and “CSG-ID”. Inthat case, in a case where a response from the SCell does not contain aCSG-ID and a CSG indication is “FALSE”, it may be judged that such anindication that the SCell does not belong to a CSG is shown. In a casewhere a response from a SCell contains a CSG-ID and a CSG indication is“TRUE”, the PCell may judge that such an indication that the SCellbelongs to a CSG is shown. In a case where a response from a SCellcontains a CSG-ID and a CSG indication is “FALSE”, the PCell may judgethat such an indication that the SCell belongs to a CSG is shown.

The PCell may inquire about “CSG-ID” in place of inquiring about“whether or not belonging to the CSG” and “CSG-ID”. In that case, in acase where a response from a SCell does not contain a CSG-ID, the PCellmay judge that that such an indication that the SCell does not belong toa CSG is shown. Meanwhile, in a case where a response from a SCellcontains a CSG-ID, the PCell may judge that that such an indication thatthe SCell belongs to a CSG is shown.

(2) Each cell notifies the control unit of the base station of “whetheror not the own cell belongs to a CSG” and, in a case where the own cellbelongs to the CSG, notifies “CSG-ID”. Before determining to configure acell as a SCell, a PCell selects a SCell candidate cell. The PCellinquires the control unit about whether or not a SCell candidate cellbelongs to the CSG and about a CSG-ID to which the SCell candidate cellbelongs. In place of inquiring about “whether or not belonging to theCSG” and about “CSG-ID”, the PCell may inquire about “CSG indication”and “CSG-ID”. The information shown by the combination of “CSGindication” and “CSG-ID” is similar to that of the specific example (1)described above. Alternatively, the PCell may inquire about “CSG-ID” inplace of inquiring about “whether or not belonging to the CSG” and“CSG-ID”. The information shown by “CSG-ID” is similar to that of thespecific example (1) described above.

(3) Each cell notifies another cell of “whether or not the own cellbelongs to a CSG” and, in a case where the own cell belongs to the CSG,notifies “CSG-ID”. In place of notifying “whether or not belonging tothe CSG” and “CSG-ID”, each cell may notify “CSG indication” and“CSG-ID”. The information shown by the combination of “CSG indication”and “CSG-ID” is similar to that of the specific example (1) describedabove. Alternatively, each cell may notify “CSG-ID” in place ofnotifying “whether or not belonging to the CSG” and “CSG-ID”. Theinformation shown by “CSG-ID” is similar to that of the specific example(1) described above.

“Whether or not belonging to the CSG” in the specific examples (1) to(3) may be “indication of belonging to a CSG” or “indication of notbelonging to the CSG”.

A specific example of the timing at which “whether or not belonging tothe CSG” and “CSG-ID” are notified is similar to the specific example ofthe timing at which “SCell use configuration” is notified in the firstmodification of the second embodiment described above, which is notdescribed here.

The PCell may select a SCell candidate cell set before determining toconfigure a cell as a SCell. A specific example of the SCell candidatecell set is similar to that of the first modification of the secondembodiment described above, which is not described here.

A specific example of the operation of the user equipment is disclosedbelow. The user equipment omits CSG access restriction on a cell whoseconfiguration content has been notified as a SCell, similarly to theaccess control on a PCell. The following three (1) to (3) are disclosedas specific examples of the method in which a user equipment omits CSGaccess restriction.

(1) Even in a case where the configuration content as a SCell containsthe CSG-indication and CSG-ID of a SCell, the user equipment does notperform access restriction using the CSG-indication and CSG-ID. Forexample, the CSG-ID of the SCell contained in the configuration contentas a SCell and the CSG-ID in the USIM of the user equipment are notcompared with each other. Alternatively, through the configuration as aSCell, the CSG-indication and CSG-ID of the SCell may not be notified.

(2) Access control using the CSG-indication and CSG-ID, which arebroadcast from the cell configured as a SCell using the broadcastinformation, is not performed. For example, the CSG-ID broadcast fromthe cell configured as a SCell using the broadcast information and theCSG-ID in the USIM of the user equipment are not compared with eachother. Alternatively, the CSG-ID broadcast from the cell configured as aSCell using the broadcast information may not be received or may beignored. Alternatively, the SIB1 broadcast from the cell configured as aSCell may not be received or may be ignored. Alternatively, the SIBbroadcast from the cell configured as a SCell may not be received or maybe ignored. Alternatively, the broadcast information broadcast from thecell configured as a SCell may not be received or may be ignored.

(3) Combination of (1) and (2) described above.

Next, a specific example of a sequence of a communication system in athird embodiment is described with reference to FIG. 16. FIG. 16 is adiagram showing an example of the sequence of the communication systemin the third embodiment. The processes of Steps ST1401 to ST1416 of FIG.14 in the third embodiment are similar to those of the secondembodiment, which are not illustrated and described here. Illustrationand description are given from the process of Step ST1417 of FIG. 14.The sequence shown in FIG. 16 is similar to the sequences shown in FIGS.14 and 15, where the same steps are denoted by the same step numbers andcommon description is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell1 of the base station A as thebest cell and camps on the cell to start communication, and thereafter,the cell2 is configured as a SCell. A case in which each cell notifiesthe control unit of the base station of “whether or not the own cellbelongs to a CSG” and, if the own cell belongs to the CSG, notifies“CSG-ID” is disclosed as a specific example of the method in which aPCell knows whether or not another cell belongs to a CSG and knows aCSG-ID to which another cell belongs. The case of the time when a basestation is installed is disclosed as a specific example of the timing atwhich “whether or not belonging to the CSG” and “CSG-ID” are notified.

In Step ST1501, a base station is installed. In this operation example,the base station A providing a plurality of cells (CCs) including thecell and cell2 is installed.

In Steps ST1601 and ST1602, each cell of the base station notifies thecontrol unit of the base station of the configuration of the own cell.The configuration of the own cell contains “whether or not belonging tothe CSG” and, in a case where the own cell belongs to the CSG, furthercontains a “CSG-ID”. In this operation example, in Step ST1601, the cellnotifies the control unit of “whether or not the cell1 being the owncell belongs to the CSG” and, in a case where the cell belongs to theCSG, notifies “CSG-ID” of the cell1. In Step ST1602, the cell2 notifiesthe control unit of “whether or not the cell2 being the own cell belongsto a CSG” and, in a case where the cell2 belongs to the CSG, notifies“CSG-ID” of the cell2.

Then, the processes of Steps ST1401 to ST1407 shown in FIG. 14 describedabove are performed, so that the UE selects the cell of the base stationA as the best cell and camps on the cell1. Then, the processes of StepsST1408 to ST1416 shown in FIG. 14 described above are performed, andthen, the process moves to Step ST1417.

In Step ST1417, the cell being a PCell starts communication with the UE.In this operation example, the cell starts communication with the UE asa PCell.

In Step ST1504, the cell being a PCell selects another cell as a SCellcandidate. In this operation example, the cell serving as a PCellselects the cell2 as a SCell candidate.

In Step ST1603, the cell being a PCell inquires the control unit aboutthe configuration of the cell being a SCell candidate selected in StepST1504. The cell being a PCell may inquire the control unit about“whether or not the SCell candidate cell belongs to a CSG” and, in thecase of belonging to a CSG, “CSG-ID”. In this operation example, thecell being a PCell inquires the control unit about “whether or not thecell2 selected as a SCell candidate belongs to a CSG” and, in the caseof belonging to the CSG, inquires about “CSG-ID”.

In Step ST1604, the control unit responds to the inquiry from the cellbeing a PCell in Step ST1603. The control unit may notify the cell beinga PCell of “whether or not an inquiry target cell belongs to a CSG” and,in the case of belonging to the CSG, may inquire about “CSG-ID. In thisoperation example, the control unit notifies the cell1 being a PCell of“whether or not the cell2 being an inquiry target cell belongs to a CSG”and, in the case of belonging to the CSG, notifies “CSG-ID”.

In Step ST1605, the cell being a PCell judges whether or not the cellbeing a SCell candidate selected in Step ST1504 belongs to the CSG. Inthis judgment, the response results to the inquiry received from thecontrol unit in Step ST1604 are used. In a case of judging that the cellbeing a SCell candidate selected in Step ST1504 belongs to the CSG inStep ST1605, the cell being a PCell moves to Step ST1606. In a case ofjudging that the cell being a SCell candidate selected in Step ST1504does not belong to the CSG, the cell being a PCell moves to, forexample, Step ST1508, which is not specific to the present embodiment.

In Step ST1606, the cell being a PCell judges whether or not the CSG towhich the cell being a SCell candidate selected in Step ST1504 isidentical to the CSG to which the own cell belongs. In this judgment,the response results to the inquiry received from the control unit inStep ST1604 are used.

In a case of judging that the CSG (CSG-ID_SCell candidate) to which thecell being a SCell candidate selected in Step ST1504 belongs isidentical to the CSG (CSG-ID_cell1) to which the own cell belongs inStep ST1606, the cell being a PCell moves to Step ST1508. In a case ofjudging that the CSG to which the cell being a SCell candidate selectedin Step ST1504 belongs differs from the CSG to which the own cellbelongs, the cell being a PCell returns to Step ST1504 to select anothercell as a SCell candidate.

Through the processes of Steps ST1605 and ST1606, only a cell (CC)belonging to the same CSG as that of the PCell can be configured as aSCell, which is specific to the present embodiment.

In Step ST1508, the cell being a PCell determines to configure the cellbeing a SCell candidate as a SCell. In this operation example, the cellbeing a PCell determines to configure the cell2 being a SCell candidateas a SCell. In the present embodiment, CSG access restriction is omittedassuming that it is similar to access control for a user equipment viathe PCell in the decision of a SCell. Specifically, in the determinationof a SCell in Step ST1508, the processes corresponding to Steps ST1410to ST1415 shown in FIG. 14 described above are not performed.

Next, another specific example of the sequence of the communicationsystem in the third embodiment is described with reference to FIG. 17.FIG. 17 is a diagram showing another example of the sequence of thecommunication system in the third embodiment. The processes of StepsST1401 to ST1416 of FIG. 14 in the third embodiment are similar to thoseof the second embodiment, which are not illustrated and described here.Illustration and description are given from the process of Step ST1417of FIG. 14. The sequence shown in FIG. 17 is similar to the sequencesshown in FIGS. 14 to 16, where the same steps are denoted by the samestep numbers and common description is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell1 of the base station A as thebest cell and camps on the cell to start communication, and thereafter,the cell2 is configured as a SCell. A case in which each cell notifiesthe control unit of the base station of “CSG-ID” of the own cell isdisclosed as a specific example of the method in which a PCell knowswhether or not another cell belongs to a CSG and knows a CSG-ID to whichanother cell belongs. The case of the time when a base station isinstalled is disclosed as a specific example of the timing at which“CSG-ID” is notified.

In Steps ST1701 and ST1702, each cell of the base station notifies thecontrol unit of the base station of the configuration of the own cell.The configuration of the own cell contains “CSG-ID” in a case where theown cell belongs to the CSG. In this operation example, in a case ofbelonging to the CSG, the cell notifies the control unit of “CSG-ID” ofthe cell in Step ST1701. In a case of belonging to the CSG, the cell2notifies the control unit of “CSG-ID” of the cell2 In Step ST1702.

In Step ST1703, the cell being a PCell inquires the control unit aboutthe configuration of the cell being a SCell candidate selected in StepST1504. The cell being a PCell may inquire the control unit about“CSG-ID” in a case of belonging to the CSG of the SCell candidate. Inthis operation example, the cell being a PCell inquires the control unitabout “CSG-ID” in a case of belonging to the CSG of the cell2 selectedas a SCell candidate.

In Step ST1704, the control unit responds to the inquiry from the cellbeing a PCell in Step ST1703. The control unit may notify the cell beinga PCell of “CSG-ID” in a case of belonging to the CSG of an inquirytarget cell. In this operation example, the control unit notifies thecell being a PCell of “CSG-ID” of the cell2 being an inquiry target cellin a case that the cell2 belongs to the CSG.

In Step ST1705, the cell being a PCell judges whether or not the cellbeing a SCell candidate selected in Step ST1504 has a CSG-ID. In otherwords, the cell being a PCell judges whether or not the SCell belongs toa CSG. In this judgment, the response results to the inquiry receivedfrom the control unit in Step ST1704 are used.

In a case of judging that the cell being a SCell candidate selected inStep ST1504 has a CSG-ID in Step ST1705, the cell being a PCell moves toStep ST1606. In other words, in a case of judging that the cell being aSCell candidate selected in Step ST1504 has a CSG-ID in Step ST1705, thecell being a PCell judges that the cell being a SCell candidate belongsto the CSG and moves to Step ST1606.

In a case of judging that the cell being a SCell candidate selected inStep ST1504 does not have a CSG-ID in Step ST1705, the cell being aPCell moves to, for example, Step ST1508, which is not specific to thepresent embodiment. In other words, in a case of judging that the cellbeing a SCell candidate selected in Step ST1504 does not have a CSG-IDin Step ST1705, the cell being a PCell judges that the cell being aSCell candidate does not belong to the CSG and moves to, for example,Step ST1508, which is not specific to the present embodiment.

Through the processes of Steps ST1705 and ST1606, only a cell (CC)belonging to the same CSG as that of the PCell can be configured as aSCell, which is specific to the present embodiment.

The third embodiment described above can achieve the following effectsin addition to the effects of the second embodiment. Also as to theSCell, subscribers who are allowed to use can be specified by anoperator. The SCell belongs to the CSG, whereby a user-friendlycommunication system can be constructed, in which wishes of users aretaken into consideration, such as services that users want to receive orcharging setting that users want to apply for.

The present embodiment can be used in combination with the firstembodiment, second embodiment, and first modification of the secondembodiment described above.

Fourth Embodiment

A fourth embodiment discloses another solution to the same problem asthat of the third embodiment described above. The solution in the fourthembodiment is described below. The present embodiment mainly describes aportion different from the solution in the second embodiment describedabove, and a portion not to be described is similar to the secondembodiment.

The base station cannot configure a cell (CC) belonging to a CSG as aSCell. The base station may render the cell (CC) belonging to the CSGinactive as a SCell. The base station can configure a cell (CC) notbelonging to the CSG as a SCell. The base station may render the cell(CC) not belonging to the CSG active as a SCell.

The use of the solution in the present embodiment enables to prevent auser equipment unregistered with a CSG to which a cell belongs fromusing the resource of that cell as a SCell.

Further, the following may be done. A base station cannot configure acell operating in a closed access mode as a SCell among the cells (CCs)belonging to the CSG. The base station may render a cell operating in aclosed access mode inactive as a SCell among the cells (CCs) belongingto a CSG.

The base station can configure as a SCell, a cell (CC) not belonging tothe CSG, a cell (CC) operating in an open access mode among the cells(CCs) belonging to the CSG, or a cell (CC) operating in a hybrid accessmode among the cells (CCs) belonging to the CSG. The base station mayrender active as a SCell, a cell (CC) not belonging to the CSG, a cell(CC) operating in an open access mode among the cells (CCs) belonging tothe CSG, or a cell (CC) operating in a hybrid access mode among thecells (CCs) belonging to the CSG.

As described above, if even access modes of cells belonging to the CSGare taken into consideration, cells that can be configured as a SCellincreases compared with the above-mentioned method in which access modesare not taken into consideration. This enables to prevent a userequipment unregistered with the CSG to which a cell belongs from using aresource of the cell as a SCell while more easily improving a data rateusing carrier aggregation compared with the above-mentioned method inwhich access modes are not taken into consideration.

The following is disclosed as a specific example of the operation of theMME. The MME regards access control for a user equipment via a cellconfigured as a SCell by a base station as access not from a userequipment via a CSG cell, and does not perform access control. The MMEmay regard the access control from a user equipment via a CSG cellconfigured as a SCell by a base station as access not from a userequipment via a CSG cell operating in a closed access mode and may notperform access control. The MME may perform only access control for auser equipment via a PCell. The MME may perform only access control froma user equipment via a PCell belonging to a CSG. The MME may onlyperform access control for a user equipment via a PCell being a CSGcell.

The following three (1) to (3) are disclosed as specific examples of themethod in which a PCell knows whether or not another cell belongs to aCSG and, in a case where another cell belongs to the CSG, an accessmode. Hereinafter, an access mode may be referred to as “operationmode”.

(1) Before determining to configure a cell as a SCell, a PCell selects aSCell candidate cell. The PCell inquires the SCell candidate cell aboutwhether or not the SCell candidate cell belongs to a CSG and, in a casewhere the SCell candidate cell belongs to a CSG, an operation mode.

The PCell may inquire about “CSG indication” and “CSG-ID” in place ofinquiring about “whether or not belonging to the CSG” and “operationmode”. In that case, if a response from the SCell does not contain aCSG-ID and a CSG indication is “FALSE”, the PCell may judge that anindication that the SCell does not belong to a CSG or an indication theSCell belongs to a CSG and operates in an open access mode is shown.

In a case where the response from the SCell contains a CSG-ID and a CSGindication is “TRUE”, the PCell may judge that it is shown that theSCell operates in a closed access mode in a case of belonging to a CSG.In a case where the response from the SCell includes a CSG-ID and a CSGindication is “FALSE”, it may be judged that the SCell belongs to a CSGand operates in a hybrid access mode is shown.

(2) Each cell notifies the control unit of the base station of “whetheror not the own cell belongs to a CSG” and, in a case where the own cellbelongs to the CSG, notifies “CSG-ID”. Before determining to configure acell as a SCell, a PCell selects a SCell candidate cell. The PCellinquires the control unit about whether or not a SCell candidate cellbelongs to a CSG and about an operation mode in a case where the SCellcandidate cell belongs to the CSG. In place of inquiring about “whetheror not belonging to the CSG” and about “operation mode”, the PCell mayinquire about “CSG indication” and “CSG-ID”. The information shown bythe combination of “CSG indication” and “CSG-ID” is similar to that ofthe specific example (1) described above.

(3) Each cell notifies another cell of “whether or not the own cellbelongs to a CSG” and, in a case where the own cell belongs to the CSG,notifies “operation mode”. In place of notifying “whether or notbelonging to the CSG” and “operation mode”, each cell may notify “CSGindication” and “CSG-ID”. The information shown by the combination of“CSG indication” and “CSG-ID” is similar to that of the specific example(1) described above.

“Whether or not belonging to a CSG” in the specific examples (1) to (3)may be “indication of belonging to a CSG” or “indication of notbelonging to the CSG”.

A specific example of the timing at which “whether or not belonging tothe CSG” and “operation mode” is similar to the specific example of thetiming at which “SCell use configuration” is notified in the firstmodification of the second embodiment described above, which is notdescribed here.

The PCell may select a SCell candidate cell set before determining toconfigure a cell as a SCell. A specific example of a SCell candidatecell set is similar to that of the first modification of the secondembodiment described above, which is not described here.

A specific example of the operation of a user equipment is describedbelow. The user equipment regards that a cell whose configurationcontent as a SCell has been notified is not a cell belonging to the CSG,and omits CSG access control, that is, CSG access restriction, in a userequipment. The user equipment may regard that a cell whose configurationcontent as a SCell has been notified is not a cell belonging to a CSGoperating in a closed access mode and omit CSG access control, that is,CSG access restriction, in a user equipment. A specific example of themethod in which a user equipment omits CSG access restriction is similarto that of the third embodiment described above, which is not describedhere.

Next, a specific example of a sequence of a communication system in thefourth embodiment is described with reference to FIG. 18. FIG. 18 is adiagram showing an example of the sequence of the communication systemin the fourth embodiment. The processes of Steps ST1401 to ST1416 ofFIG. 14 in the fourth embodiment are similar to those of the secondembodiment, which are not illustrated and described here. Illustrationand description are given from the process of Step ST1417 of FIG. 14.The sequence shown in FIG. 18 is similar to the sequences shown in FIGS.14 and 15, where the same steps are denoted by the same step numbers andcommon description is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where a UE selects the cell1 of the base station A as the bestcell and camps on the cell1 to start communication, and thereafter, thecell2 is configured as a SCell. As a specific example of the method inwhich a PCell knows whether or not another cell belongs to a CSG andknows an operation mode in a case where another cell belongs to the CSG,a case in which each cell notifies the control unit of the base stationof “whether or not the own cell belongs to a CSG” and “operation mode”in a case of belonging to the CSG is disclosed. The case of the timewhen a base station is installed is disclosed as a specific example ofthe timing at which “whether or not belonging to the CSG” and “operationmode” are notified.

In Step ST1501, a base station is installed. In this operation example,the base station A providing a plurality of cells (CCs) including thecell1 and the cell2 is installed.

In Steps ST1801 and ST1802, each cell of the base station notifies thecontrol unit of the base station of the configuration of the own cell.The configuration of the own cell includes “whether or not belonging tothe CSG” and “operation mode” in a case of belonging to the CSG. In thisoperation example, in Step ST1801, the cell notifies the control unit of“whether or not the cell belongs to a CSG” and “operation mode” in acase of belonging to the CSG. In Step ST1802, the cell2 notifies thecontrol unit of “whether or not the cell2 belongs to a CSG” and“operation mode” in a case of belonging to the CSG.

Then, the processes of Steps ST1401 to ST1407 shown in FIG. 14 describedabove are performed, so that the UE selects the cell of the base stationA as the best cell and camps on the cell1. Then, the processes of StepsST1408 to ST1416 shown in FIG. 14 described above are performed, andthen, the process proceeds to Step ST1417.

In Step ST1417, the cell being a PCell starts communication with the UE.In this operation example, the cell starts communication with the UE asa PCell.

In Step ST1504, the cell being a PCell selects another cell as a SCellcandidate. In this operation example, the cell serving as a PCellselects the cell2 as a SCell candidate.

In Step ST1803, the cell being a PCell inquires the control unit aboutthe configuration of the cell being a SCell candidate selected in StepST1504. The cell being a PCell may inquire the control unit about“whether or not the SCell candidate belongs to a CSG” and “operationmode” in a case of belonging to a CSG. In this operation example, thecell being a PCell inquires the control unit about “whether or not thecell2 selected as a SCell candidate belongs to a CSG” and “operationmode” in a case of belonging to the CSG.

In Step ST1804, the control unit responds to the inquiry from for thecell being a PCell in Step ST1803. The control unit may notify the cellbeing a PCell of “whether or not an inquiry target cell belongs to aCSG” or “operation mode” in a case of belonging to the CSG. In thisoperation example, the control unit notifies the cell1 being a PCell of“whether or not the cell2 being an inquiry target cell belongs to a CSG”and “operation mode” in a case of belonging to the CSG.

In Step ST1805, the cell being a PCell judges whether or not the cellbeing a SCell candidate selected in Step ST1504 belongs to a CSG. Inthis judgment, the response results to the inquiry received from thecontrol unit in Step ST1804 are used.

In a case of judging that the cell being a SCell candidate selected inStep ST1504 belongs to the CSG in Step ST1805, the cell being a PCellmoves to Step ST1806. In a case of judging that the cell being a SCellcandidate selected in Step ST1504 does not belong to the CSG in StepST1805, the cell being a PCell moves to Step ST1508.

In Step ST1806, the cell being a PCell judges whether or not theoperation mode of the cell being a SCell candidate selected in StepST1504 is a closed access mode. In this judgment, the response resultsto the inquiry received from the control unit in Step ST1804 are used.

In a case of judging that the operation mode of the cell being a SCellcandidate selected in Step ST1504 is not a closed access mode in StepST1806, the cell being a PCell moves to Step ST1508. That is, in a caseof judging that the operation mode of the cell being a SCell candidateselected in Step ST1504 is an open access mode or hybrid access mode inStep ST1806, the cell being a PCell moves to Step ST1508.

In a case of judging that the operation mode of the cell being a SCellcandidate selected in Step ST1504 is a closed access mode in StepST1806, the cell being a PCell returns to Step ST1504 to select anothercell as a SCell candidate.

Through the processes of Steps ST1805 and ST1806, a cell (CC) notbelonging to the CSG can be configured as a SCell, which is specific tothe present embodiment. Alternatively, a cell (CC) not belonging to theCSG, a cell (CC) operating in an open access mode among the cells (CCs)belonging to the CSG, or a cell (CC) operating in a hybrid access modeamong the cells (CCs) belonging to the CSG can be configured as a SCell.

In Step ST1508, the cell being a PCell determines to configure the cellbeing a SCell candidate as a SCell. In this operation example, the cell1being a PCell determines to configure the cell2 being a SCell candidateas a SCell. In the present embodiment, in determination of a SCell, CSGaccess restriction is omitted assuming that the access is not from auser equipment via a CSG cell or that even if the access is from a userequipment via a CSG cell, which is not from an equipment via a CSG celloperating in a closed access mode. Specifically, the processescorresponding to Steps ST1410 to ST1415 are not performed indetermination of a SCell in Step ST1508.

Next, another specific example of the sequence of the communicationsystem in the fourth embodiment is described with reference to FIG. 19.FIG. 19 is a diagram showing another example of the sequence of thecommunication system in the fourth embodiment. The processes of StepsST1401 to ST1416 of FIG. 14 in the fourth embodiment are similar tothose of the second embodiment, which are not illustrated and describedhere. Illustration and description are given from the process of StepST1417 of FIG. 14. The sequence shown in FIG. 19 is similar to thesequences shown in FIGS. 14, 15, and 18, where the same steps aredenoted by the same step numbers and common description is not givenhere.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell1 and a cell2 ispresent, where a UE selects the cell1 of the base station A as the bestcell and camps on the cell to start communication, and then, the cell2is configured as a SCell. As a specific example of the method in which aPCell knows whether or not another cell belongs to a CSG and knows anoperation mode in a case where another cell belongs to the CSG, a casein which each cell notifies the control unit of the base station of “CSGindication” and “CSG-ID” of the own cell is disclosed. The case of thetime when a base station is installed is disclosed as a specific exampleof the timing at which “CSG indication” and “CSG-ID” are notified.

In Steps ST1901 and ST1902, each cell of the base station notifies thecontrol unit of the base station of the configuration of the own cell.The configuration of the own cell includes “CSG indication” and“CSG-ID”. In this operation example, in Step ST1901, the cell notifiesthe control unit of “CSG indication” and “CSG-ID” of the cell1. In StepST1902, the cell2 notifies the control unit of “CSG indication” and“CSG-ID” of the cell2.

In Step ST1903, the cell being a PCell inquires the control unit aboutthe configuration of the cell being a SCell candidate selected in StepST1504. The cell being a PCell may inquire the control unit about “CSGindication” and “CSG-ID” of the SCell candidate. In this operationexample, the cell being a PCell inquires the control unit about “CSGindication” and “CSG-ID” of the cell2 selected as a SCell candidate.

In Step ST1904, the control unit responds to the inquiry from the cellbeing a PCell in Step ST1903. The control unit may notify the cell beinga PCell of “CSG indication” and “CSG-ID” of the inquiry target cell. Inthis operation example, the control unit notifies the cell being a PCellof “CSG indication” and “CSG-ID” of the cell2 being an inquiry targetcell.

In Step ST1905, the cell being a PCell judges whether or not the cellbeing a SCell candidate selected in Step ST1504 has a CSG-ID. In otherwords, the cell being a PCell judges whether or not the SCell belongs tothe CSG. In this judgment, the response results to the inquiry receivedfrom the control unit in Step ST1904 are used.

In a case of judging that the cell being a SCell candidate selected inStep ST1504 has a CSG-ID in Step ST1905, the cell being a PCell moves toStep ST1906. In other words, in a case of judging that the cell being aSCell candidate selected in Step ST1504 has a CSG-ID in Step ST1905, thecell being a PCell judges that the cell being a SCell candidate belongsto the CSG, and then moves to Step ST1906.

In a case of judging that the cell being a SCell candidate selected inStep ST1504 does not have a CSG-ID in Step ST1905, the cell being aPCell moves to Step ST1508. In other words, in a case of judging thatthe cell being a SCell candidate selected in Step ST1504 does not have aCSG-ID in Step ST1905, the cell being a PCell judges that the cell beinga SCell candidate does not belong to the CSG, and then moves to StepST1508.

In Step ST1906, the cell being a PCell judges whether or not the CSGindication of the cell being a SCell candidate selected in Step ST1504is “TRUE”. In other words, the cell judges whether or not the accessmode of the SCell is a closed access mode. In this judgment, theresponse results to the inquiry received from the control unit in StepST1904 are used.

In a case of judging that the CSG indication of the cell being a SCellcandidate selected in Step ST1504 is not “TRUE”, that is, is “FALSE” inStep ST1906, the cell being a PCell moves to Step ST1508. In otherwords, in a case of judging that the operation mode of the cell being aSCell candidate selected in Step ST1504 is an open access mode or hybridaccess mode in Step ST1906, the cell being a PCell moves to Step ST1508.

In a case of judging that the CSG indication of the SCell candidateselected in Step ST1504 is “TRUE” in Step ST1906, the cell being a PCellreturns to Step ST1504 to select another cell as a SCell candidate. Inother words, in a case of judging that the operation mode of the cellbeing a SCell candidate selected in Step ST1504 is a closed access modein Step ST1906, the cell being a PCell returns to Step ST1504 to selectanother cell as a SCell candidate.

Through the processes of Steps ST1905 and ST1906, a cell (CC) notbelonging to the CSG can be configured as a SCell, which is specific tothe present embodiment. Alternatively, a cell (CC) not belonging to theCSG, a cell (CC) operating in an open access mode among the cells (CCs)belonging to the CSG, or a cell (CC) operating in a hybrid access modeamong the cells (CCs) belonging to the CSG can be configured as a SCell.

The fourth embodiment described above can achieve the following effectsin addition to the effects of the second embodiment. Also as to theSCell, subscribers who are allowed to use can be specified by anoperator. The SCell belongs to the CSG, whereby a user-friendlycommunication system can be constructed, in which wishes of users aretaken into consideration, such as services that users want to receive orcharging setting that users want to apply for.

The present embodiment can be used in combination with the firstembodiment, second embodiment, first modification of the secondembodiment, and third embodiment descried above.

Fifth Embodiment

A fifth embodiment discloses another solution to the same problem of thethird embodiment described above, that is, a problem that occurs in acase where the second embodiment described above is used. The presentembodiment solves the problem of the second embodiment described aboveby a method different from the solution of the second embodiment.

Before determining to configure a cell as a SCell, a PCell selects aSCell candidate cell. The cell being a PCell notifies a user equipmentof the configuration content of the SCell candidate cell. The userequipment that has received the configuration content of the SCellcandidate cell performs CSG access restriction on a cell whoseconfiguration content has been notified as a SCell candidate cell. Theuser equipment notifies the PCell of the judgment results of CSG accessrestriction. The PCell that has received the judgment results determinesa SCell based on the judgment results.

The PCell may select a SCell candidate cell set before determining toconfigure a cell as a SCell. The contents of the configuration of theSCell candidate cell which are notified a user equipment by a PCell maybe the configuration content of the SCell candidate cell set.Alternatively, CSG access restriction that is performed by a userequipment may be directed to a SCell candidate cell set. A specificexample of the SCell candidate cell set is similar to that of the firstmodification of the second embodiment described above, which is notdescribed here.

With the use of the solution of the present embodiment, a user equipmentperforms CSG access restriction on a SCell. This enables to prevent acell belonging to a CSG with which a user equipment has beenunregistered from being configured as a SCell for the user equipmentwhile improving a data rate using carrier aggregation. Accordingly, itis possible to prevent a user equipment unregistered with a CSG to whicha cell belongs from using a resource of the cell as a SCell.

A specific example of the operation of a user equipment is disclosedbelow. The user equipment performs CSG access restriction on a cellwhose configuration content has been notified as a SCell candidate cell.The user equipment may perform CSG access restriction in a case wherethe SCell candidate cell is a CSG cell. The following three (1) to (3)are disclosed as specific examples of the method in which a userequipment performs CSG access restriction.

(1) A user equipment performs access restriction with the CSG-indicationand CSG-ID of the SCell candidate cell in the configuration content as aSCell candidate cell. For example, the CSG-ID of the SCell candidatecell contained in the configuration content as a SCell candidate celland the CSG-ID in the USIM of the user equipment are compared. In a casewhere the CSG-ID of the SCell candidate cell contained in theconfiguration content as a SCell candidate cell is contained in thewhitelist of, for example, the USIM of the user equipment as a result ofthe comparison, it is judged that access is allowed. Meanwhile, in acase where the CSG-ID of the SCell candidate cell contained in theconfiguration content as a SCell candidate cell is not contained in thewhitelist of the USIM of the user equipment as a result of thecomparison, it is judged that access is not allowed.

(2) A user equipment performs access restriction with the CSG-indicationand CSG-ID broadcast from a cell configured as a SCell candidate cellusing the broadcast information. For example, the CSG-ID broadcast froma cell configured as a SCell candidate cell using the broadcastinformation and the CSG-ID in the USIM of the user equipment arecompared. In a case where the CSG-ID broadcast from the cell configuredas a SCell candidate cell using the broadcast information is containedin the whitelist of, for example, the USIM of the user equipment, it isjudged that access is allowed. Meanwhile, in a case where the CSG-IDbroadcast from the cell configured as a SCell candidate cell using thebroadcast information is not contained in the whitelist of, for example,the USIM of the user equipment, it is judged that access is not allowed.

(3) Combination of (1) and (2) above.

The following three (1) to (3) are disclosed as specific examples of theconditions when a user equipment notifies a PCell of the judgmentresults of CSG access restriction.

(1) A user equipment makes a notification in a case of having performedCSG access restriction. In this specific example, the judgment resultsare always notified. This makes it easier to detect a communicationerror occurring in a radio area. Accordingly, an effect that a systemmore resistant to a communication error can be constructed compared withthe specific examples (2) and (3) can be achieved.

(2) A user equipment makes a notification in a case where the judgmentresults of CSG access restriction show “access is not allowed”. In acase of not receiving the judgment results of CSG access restrictionfrom a user equipment for a certain period, the PCell may judge that thejudgment results of CSG access restriction show “access is allowed”. Inthis specific example, an effect that a radio resource can be used moreeffectively compared with the specific example (1) can be achieved.

(3) A user equipment makes a notification in a case where the judgmentresults of CSG access restriction show “access is allowed”. In a case ofnot receiving the judgment results of CSG access restriction from a userequipment for a certain period, the PCell may judge that the judgmentresults of CSG access restriction show “access is not allowed”. In thisspecific example, an effect that a radio resource can be used moreeffectively compared with the specific example (1) can be achieved.

A specific example of the method in which a user equipment notifies aPCell of the judgment results of CSG access restriction is described.The user equipment notifies the PCell of the judgment results of CSGaccess restriction through RRC signaling or using an RRC message.

The following two (1) and (2) are disclosed as specific examples of themethod in which a user equipment notifies a PCell of the judgmentresults of CSG access restriction using an RRC message.

(1) RRC signaling or RRC message is newly provided. Parameters to bemapped to the newly-provided RRC signaling are the judgment results ofCSG access restriction. The judgment results of CSG access restrictionmay be notified together with a user equipment identifier. The userequipment identifier may be UE-ID or IMSI.

(2) Existing RRC signaling or RRC message is used. The parametersrequired to be added to the existing RRC signaling are the judgmentresults of CSG access restriction. The specific example (2) is moreeffective than the specific example (1) in that signaling is notrequired to be newly provided, whereby a communication system can beprevented from becoming complex.

Next, a specific example of the method in which a user equipmentnotifies the judgment results of CSG access restriction with theexisting RRC signaling is disclosed below. The method disclosed inNon-Patent Document 2 is used. Specifically, the method of responding to“RRC Connection Reconfiguration message” of RRC signaling, which isstudied to be used in addition or modification of a SCell, is used.

The existing method of responding to “RRC Connection Reconfigurationmessage” is described. In a case where the user equipment hassuccessfully finished the reconfiguration instructed by “RRC ConnectionReconfiguration message”, the user equipment notifies a base station of“RRC Connection Reconfiguration complete”. In a case where the userequipment has not successfully finished the reconfiguration instructedby “RRC Connection Reconfiguration message”, the user equipment notifiesthe base station of “RRC Connection reestablishment REQUEST” forrequesting RRC connection re-establishment.

A specific example of a case in which the existing responding method isused is disclosed below. In a case where the judgment results of CSGaccess restriction show “access is allowed”, the user equipmentrecognizes that the reconfiguration instructed by “RRC ConnectionReconfiguration message” has been successfully finished, and thennotifies a PCell of “RRC Connection Reconfiguration complete”. Uponnotification of “RRC Connection Reconfiguration complete”, if thejudgment results of CSG access restriction show “access is allowed”, itis not required to newly provide RRC signaling and to add newparameters. This enables to construct a communication system havingexcellent backward compatibility.

Alternatively, parameters being the judgment results of CSG accessrestriction may be added to “RRC Connection Reconfiguration message”.Accordingly, the judgment results of CSG access restriction can beexplicitly notified. This allows explicit distinction from “RRCConnection Reconfiguration complete” in a case where the judgmentresults of CSG access restriction are not notified, to thereby achievean effect that a stable communication system can be constructed.

Meanwhile, in a case where the judgment results of CSG accessrestriction show “access is not allowed”, the existing method ofresponding to “RRC Connection Reconfiguration message” suffers from adrawback described below. In the existing responding method, in a casewhere the reconfiguration instructed by “RRC Connection Reconfigurationmessage” has been not successfully finished, “RRC Connectionreestablishment REQUEST” is notified as described above.

Note that if the judgment results of CSG access restriction show “accessis not allowed”, there is no problem in RRC connection with a PCell,which does not require RRC connection re-establishment. Therefore, in acase where the judgment results of CSG access restriction show “accessis not allowed”, a user equipment does not notify a PCell of “RRCConnection reestablishment REQUEST” though it has not successfullyfinished the reconfiguration instructed by “RRC ConnectionReconfiguration message”. This enables to prevent unnecessary RRCconnection re-establishment, leading to an effect that control delays ofa communication system can be prevented.

The following two (a1) and (a2) are disclosed as specific examples ofthe notification method in a case where the judgment results of CSGaccess restriction show “access is not allowed”.

(a1) RRC signaling or RRC message is newly provided. A parameter to bemapped to the newly-provided RRC signaling is “access is not allowed”.

(a2) The existing RRC signaling or RRC message is used. A parameterrequired to be added to the existing RRC signaling is “access is notallowed”. The specific example (a2) is more effective than the specificexample (a1) in that signaling needs not to be newly provided, whichenables to prevent a communication system from becoming complex.Specific examples of the existing RRC signaling include “RRC ConnectionReconfiguration complete”.

A specific example of the operation of a base station is disclosedbelow. The base station selects a SCell candidate cell before a PCelldetermines to configure the SCell candidate cell as a SCell. The PCellnotifies the user equipment of the configuration content of the SCellcandidate cell. The PCell receives, from the user equipment, thejudgment results of CSG access restriction performed by the userequipment. The PCell that has received the judgment results determines aSCell based on the judgment results.

Disclosed below is a specific example in which a user equipmentdetermines a SCell based on the judgment results of CSG accessrestriction performed by the user equipment. A case in which “access isallowed” is received from the user equipment as the judgment results ofCSG access restriction performed by the user equipment is disclosed. ThePCell determines to configure a SCell candidate cell as a SCell.Alternatively, the PCell may judge that a SCell candidate cell can berendered active.

Disclosed here is a case in which “access is not allowed” is receivedfrom a user equipment as the judgment results of CSG access restrictionperformed by the user equipment. The PCell determines not to configure aSCell candidate cell as a SCell. Alternatively, the PCell determines toeliminate a SCell candidate cell from the SCell candidate cell. Stillalternatively, the PCell may judge that the SCell candidate cell cannotbe rendered active.

A specific example of the operation of an MME is disclosed below. TheMME does not perform access control for a user equipment via a cellconfigured as a SCell by the base station. The MME may recognize thataccess control by a cell configured as a SCell by the base station hasbeen finished on the user equipment side and omit CSG access control bythe MME. The MME may only perform access control for a user equipmentvia a PCell. The MME may only perform access control for a userequipment via a PCell belonging to a CSG. The MME may only performaccess control for a user equipment via a PCell being a CSG cell.

Next, a specific example of a sequence of a communication system in thefifth embodiment is described with reference to FIG. 20. FIG. 20 is adiagram showing an example of the sequence of the communication systemin the fifth embodiment. The processes of Steps ST1401 to ST1416 of FIG.14 in the fifth embodiment are similar to those of the secondembodiment, which are not illustrated and described here. Illustrationand description are given from the process of Step ST1417 of FIG. 14.The sequence shown in FIG. 20 is similar to the sequences shown in FIGS.14 and 15, where the same steps are denoted by the same step numbers andcommon description is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell1 and a cell2 ispresent, where a user equipment (UE) selects the cell1 of the basestation A as the best cell and camps on the cell to start communication,and thereafter, the cell2 is configured as a SCell.

A case in which access restriction is performed with the CSG-indicationand CSG-ID of a SCell candidate cell in the configuration content as aSCell candidate cell is disclosed as a specific example of the method inwhich a user equipment performs CSG access restriction. Disclosed belowis a case in which a user equipment performs CSG access restriction as aspecific example of the conditions when a user equipment notifies aPCell of the judgment results of CSG access restriction. A case in which“RRC Connection Reconfiguration complete” being the existing RRCsignaling is used for “access is allowed” as well as “access is notallowed” is disclosed as a specific example of the method in which auser equipment notifies a PCell of the judgment results of CSG accessrestriction.

After the processes of Steps ST1401 to ST1416 shown in FIG. 14 describedabove are performed, in Step ST1417, the cell being a PCell, which isthe cell in this operation example, starts communication with a userequipment (UE). Then, in Step ST1504, the cell being a PCell selectsanother cell as a SCell candidate. In this operation example, the cell1serving as a PCell selects the cell2 as a SCell candidate.

In Step ST2001, the cell being a PCell notifies a user equipment (UE) ofthe configuration content of the SCell candidate cell using dedicatedRRC signaling. In this operation example, the cell2 as a SCell candidatecell and the configuration content of the cell2 are notified using “RRCConnection Reconfiguration message” of dedicated RRC signaling. On thatoccasion, the system information of the cell2 is notified as well.Specifically, the information related to access to the cell2, forexample, CSG-ID_cell2 or the like is notified as a CSG identity andCSG-indication_cell2 or the like is notified as a CSG indication.

In Step ST2002, the cell2 broadcasts a SIB to user equipments beingserved thereby. Specifically, the information related to access to thecell2, for example, CSG-ID_cell2 or the like is broadcast as a CSGidentity and CSG-indication_cell2 or the like is broadcast as CSGindication. This operation example discloses a case in which accessrestriction is performed with the CSG-indication and CSG-ID of a SCellcandidate cell in the configuration content as a SCell candidate cell.Therefore, the user equipment may or may not receive the broadcastinformation from the cell2.

In Step ST2003, the user equipment (UE) judges whether or not the CSGindication in the configuration content of the SCell candidate cell thathas been received in Step ST2001 is “TRUE”. In this operation example,the user equipment judges whether or not CSG-indication_cell2 is “TRUE”.In a case of judging that the CSG indication is “TRUE” in Step ST2003,the user equipment moves to Step ST2004. In a case of judging that theCSG indication is not “TRUE”, that is, is “FALSE”, in Step ST2003, theuser equipment moves to Step ST2005.

In Step ST2004, the user equipment (UE) judges whether or not the ownuser equipment has been registered with the CSG indicated by the CSGidentity in the configuration content of the SCell candidate cell thathas been received in Step ST2001. In a case of judging that the own userequipment has been registered in Step ST2004, the user equipment movesto Step ST2005. In a case of judging that the own user equipment hasbeen unregistered in Step ST2004, the user equipment moves to StepST2006.

Through the processes of Steps ST2003 and ST2004, a user equipment canperform CSG access restriction on a cell whose configuration content hasbeen notified as a SCell candidate cell, which is specific to thepresent embodiment.

In Step ST2005, the user equipment (UE) sets “access is allowed” or“access is OK” as the judgment results of CSG access restriction. Inthis operation example, the user equipment sets “access is OK” in “RRCConnection Reconfiguration complete” as the judgment results of CSGaccess restriction.

In Step ST2006, the user equipment (UE) sets “access is not allowed” or“access is NG” as the judgment results of CSG access restriction.

In Step ST2007, the user equipment notifies the cell being a PCell of“RRC Connection Reconfiguration Complete” in response to “RRC ConnectionReconfiguration” received in Step ST2007. The user equipment may notifythe cell being a PCell of “RRC Connection Reconfiguration Complete”.“RRC Connection Reconfiguration Complete” includes the access judgmentresults set in Step ST2005 or Step ST2006.

In Step ST2008, the cell being a PCell judges whether or not thejudgment results of CSG access restriction on the cell being a SCellcandidate selected in Step ST1504 in the user equipment show that accessis allowed or OK. The PCell may judge whether or not the judgmentresults of CSG access restriction on the cell being a SCell candidate inthe user equipment show that access is not allowed. The access judgmentresults received from the user equipment in Step ST2007 are used in thisjudgment.

In a case of judging that the judgment results of CSG access restrictionon the cell being a SCell candidate selected in Step ST1504 in the userequipment show that access is allowed in Step ST2008, the cell being aPCell moves to Step ST1508. In a case of judging that the judgmentresults of CSG access restriction on the cell being a SCell candidateselected in Step ST1504 in the user equipment show that access is notallowed, the cell being a PCell returns to Step ST1504 to select anothercell as a SCell candidate. In this operation example, the cell being aPCell judges that the cell2 being a SCell candidate is accessible as aSCell, and then moves to Step ST1508.

Through the process of Step ST2008, the cell being a PCell can determinea SCell based on the judgment results of CSG access restriction by auser equipment, which is specific to the present embodiment.

The fifth embodiment described above can achieve the following effects.As in the third embodiment described above, subscribers who are allowedto use the SCell can be specified by an operator. In addition, it ispossible to configure a cell corresponding to one or a plurality ofCSG-IDs in a whitelist of a UE as SCells. Further, the SCell belongs toa CSG, whereby a user-friendly communication system can be constructed,in which wishes of users are taken into consideration, such as servicesthat users want to receive or charging setting that users want to applyfor. Besides, as in the second embodiment described above, the operationas a communication system can be stabilized while improving a data rateusing carrier aggregation, which enables to appropriately provideservices.

The present embodiment can be used in combination with the firstembodiment described above.

First Modification of Fifth Embodiment

The present modification describes a point to be further improved in thefifth embodiment described above. The present modification mainlydescribes a portion different from the solution in the fifth embodimentdescribed above, and a portion not to be described is similar to thefifth embodiment.

The PCell selects a SCell candidate cell before determining to configurea cell as a SCell. Whether or not a user equipment (UE) unregisteredwith a CSG can use each cell (CC) as a SCell can be configured. Thisconfiguration may be referred to as “SCell use configuration of a UEunregistered with a CSG”. The PCell notifies the user equipment of theconfiguration content of the SCell candidate cell and “SCell useconfiguration of a UE unregistered with a CSG” of the cell. The userequipment that has received the configuration content of the SCellcandidate cell and “SCell use configuration of a UE unregistered with aCSG” of the cell performs CSG access restriction on the SCell candidatecell also in consideration of “SCell use configuration of a UEunregistered with a CSG”.

Alternatively, the PCell selects a SCell candidate cell beforedetermining to configure a cell as a SCell. The configuration can bemade as to whether or not a user equipment (UE) unregistered with a CSGcan use each cell (CC) as a SCell. This configuration may be referred toas “SCell use configuration of a UE unregistered with a CSG”. In a casewhere “SCell use configuration of a UE unregistered with a CSG” of theSCell candidate cell is “cannot be used”, the PCell notifies the userequipment of the configuration content of the SCell candidate cell.

The user equipment that has received the configuration content of theSCell candidate cell performs CSG access restriction on a cell whoseconfiguration content has been notified as a SCell candidate cell. Theuser equipment notifies the PCell of the judgment results of CSG accessrestriction. The PCell that has received the judgment results maydetermine a SCell based on the judgment results. In other words, in acase where “SCell use configuration of a UE unregistered with a CSG” ofthe SCell candidate cell is “can be used”, the PCell may not performdetermination of a SCell based on the judgment results of CSG accessrestriction of a user equipment.

The following three (1) to (3) are disclosed as specific examples of theSCell use configuration of a UE unregistered with a CSG. (1) Whether ornot a UE unregistered with a CSG can use a cell as a SCell. (2)Indication that a UE unregistered with a CSG can use a cell as a SCell.This enables to achieve an effect of a smaller amount of informationcompared with the specific example of (1). (3) Indication that a UEunregistered with a CSG cannot use a cell as a SCell. This enables toachieve an effect of a smaller amount of information compared with thespecific example (1).

A specific example of the method in which a PCell knows “SCell useconfiguration of a UE unregistered with a CSG” of another cell issimilar to the specific example of the method in which a PCell knows“SCell use configuration” of another cell in the first modification ofthe second embodiment described above, which is not described here.

A specific example of the timing at which “SCell use configuration of aUE unregistered with a CSG” is notified is similar to the specificexample of the timing at which “SCell use configuration” is notified inthe first modification of the second embodiment described above, whichis not described here.

The PCell may select a SCell candidate cell set before determining toconfigure a cell as a SCell. The contents of the configuration of theSCell candidate cell, which are notified the user equipment by thePCell, may be the configuration content of the SCell candidate cell set.CSG access restriction performed by the user equipment may be directedto the SCell candidate cell set. A specific example of the SCellcandidate cell set is similar to that of the first modification of thesecond embodiment described above, which is not described here.

A specific example of the method in which a user equipment performs CSGaccess restriction on the SCell candidate cell also in consideration of“SCell use configuration of a UE unregistered with a CSG” is disclosedbelow. In a case where it is shown that “SCell use configuration of a UEunregistered with a CSG” can be used, a user equipment judges that aSCell candidate cell can be used as a SCell even if the UE has beenunregistered with the CSG, and does not perform CSG access restrictionon the SCell candidate cell. In a case where it is shown that “SCell useconfiguration of a UE unregistered with a CSG” cannot be used, the userequipment performs CSG access restriction.

Next, a specific example of a sequence of a communication system in thefirst modification of the fifth embodiment is described with referenceto FIG. 21. FIG. 21 is a diagram showing an example of the sequence ofthe communication system in the first modification of the fifthembodiment. The processes of Steps ST1401 to ST1416 of FIG. 14 describedabove in the first modification of the fifth embodiment are similar tothose of the second embodiment, which are not illustrated and describedhere. Illustration and description are given from the process of StepST1417 of FIG. 14. The sequence shown in FIG. 21 is similar to thesequences shown in FIGS. 14, 15, and 20, where the same steps aredenoted by the same step numbers and common description is not givenhere.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell1 and a cell2 ispresent, where the user equipment (UE) selects the cell of the basestation A as the best cell and camps on the cell1 to startcommunication, and thereafter, the cell2 is configured as a SCell.

A case in which a user equipment performs access restriction with theCSG-indication and CSG-ID of a SCell candidate cell in the configurationcontent as a SCell candidate cell is described as a specific example ofa method in which a user equipment performs CSG access restriction. Acase where a user equipment performs CSG access restriction is disclosedas a specific example of the conditions when the user equipment notifiesa PCell of the judgment results of CSG access restriction. A case inwhich “RRC Connection Reconfiguration complete” being the existing RRCsignaling is used for “access is allowed” as well as “access is notallowed” is disclosed as a specific example of the method in which auser equipment notifies a PCell of the judgment results of CSG accessrestriction.

A case in which each cell notifies the control unit of the base stationof “SCell use configuration of a UE unregistered with a CSG” of the owncell is disclosed as a specific example of the method in which a PCellknows “SCell use configuration of a UE unregistered with a CSG”. A caseof the time when a base station is installed is disclosed as a specificexample of the timing at which “SCell use configuration of a UEunregistered with a CSG” is notified.

In Step ST1501, a base station is installed. In this operation example,the base station A providing a plurality of cells (CCs) including thecell and cell2 is installed.

In Steps ST2101 and ST2102, each cell of the base station notifies thecontrol unit of the base station of the configuration of the own cell.The configuration of the own cell includes “SCell use configuration of aUE unregistered with a CSG”. In this operation example, in Step ST2101,the cell notifies the control unit of “SCell use configuration of a UEunregistered with a CSG” of the cell1. In Step ST2102, the cell2notifies the control unit of “SCell use configuration of a UEunregistered with a CSG” of the cell2.

Then, the processes of Steps ST1401 to T1407 shown in FIG. 14 describedabove are performed, so that the user equipment (UE) selects the cell1of the base station A as the best cell and camps on the cell1. Then, theprocesses of Steps ST1408 to ST1416 shown in FIG. 14 described above areperformed, and then, the process moves to Step ST1417.

In Step ST1417, the cell being a PCell starts communication with theuser equipment. In this operation example, the cell starts communicationwith the user equipment as a PCell.

In Step ST1504, the cell being a PCell selects another cell as a SCellcandidate. In this operation example, the cell serving as a PCellselects the cell2 as a SCell candidate.

In Step ST2103, the cell being a PCell inquires the control unit aboutthe configuration of the cell being a SCell candidate selected in StepST1504. The cell being a PCell may inquire the control unit about “SCelluse configuration of a UE unregistered with a CSG” of the SCellcandidate. In this operation example, the cell being a PCell inquiresthe control unit about “SCell use configuration of a UE unregisteredwith a CSG” of the cell2 selected as a SCell candidate.

In Step ST2104, the control unit responds to the inquiry from the cellbeing a PCell in Step ST2103. The control unit may notify the cell beinga PCell of “SCell use configuration of a UE unregistered with a CSG” ofthe inquiry target cell. In this operation example, the control unitnotifies the cell being a PCell of “SCell use configuration of a UEunregistered with a CSG” of the cell2 being an inquiry target cell.

In Step ST2105, the cell being a PCell notifies the user equipment ofthe SCell candidate cell and the configuration content of the SCellcandidate cell using dedicated RRC signaling. In this operation example,the cell2 as a SCell candidate cell and the configuration content of thecell2 are notified using “RRC Connection Reconfiguration message” ofdedicated RRC signaling. On that occasion, the system information of thecell2 and “SCell use configuration of a UE unregistered with a CSG” arenotified as well. Specifically, the information related to access to thecell2, for example, CSG-ID_cell2 or the like is notified as a CSGidentity and CSG-indication_cell2 or the like is notified as a CSGindication.

In Step ST2106, the cell2 broadcasts the SIB to user equipments beingserved thereby. On that occasion, “SCell use configuration of a UEunregistered with a CSG” of the cell2 may be broadcast as well.Specifically, the information related to access to the cell2, forexample, CSG-ID_cell2 or the like is broadcast as a CSG identity andCSG-indication_cell2 or the like is broadcast as a CSG indication. Thisoperation example discloses a case in which access restriction isperformed using the CSG-indication and CSG-ID of a SCell candidate cellin the configuration content as a SCell candidate cell. Therefore, theuser equipment may or may not receive the broadcast information from thecell2.

In Step ST2107, the user equipment (UE) judges whether or not the SCellcandidate cell received in Step ST2105 can be used as a SCell by a UEunregistered with the CSG. “SCell use configuration of a UE unregisteredwith a CSG” received from the cell in Step ST2105 is used in thisjudgment.

In a case of judging that the SCell candidate cell received in StepST2105 can be used as a SCell by a UE unregistered with a CSG in StepST2107, the user equipment (UE) moves to Step ST2005. In a case ofjudging that the SCell candidate cell received in Step ST2105 cannot beused as a SCell by a UE unregistered with a CSG in Step ST2107, the userequipment moves to Step ST2003.

The first modification of the fifth embodiment described above canachieve the following effects in addition to the effects of the fifthembodiment described above. Whether or not the UE unregistered with aCSG can use a cell as a SCell can be set in units of cells in a basestation. Accordingly, the cells can be operated with more precision.

The present modification can be used in combination with the firstembodiment described above.

Sixth Embodiment

A sixth embodiment describes another solution to the same problem asthat of the third embodiment described above, that is, the problemoccurring in a case where the second embodiment described above is used.The solution in the sixth embodiment is described below. The presentembodiment solves the problem in the second embodiment by a methoddifferent from the solution of the second embodiment.

A base station (cell) configures a SCell in consideration of the CSGregistration situation of the user equipment. This enables to preventthe user equipment from configuring, as a SCell, a cell belonging to aCSG with which the user equipment has been unregistered for the userequipment. Accordingly, the user equipment unregistered with the CSG towhich the cell belongs can be prevented from using the resource of thecell as a SCell while improving a data rate using carrier aggregation.The CSG registration situation of a user equipment corresponds to asituation in which a user equipment (UE) is allowed to access a SCellcandidate cell.

A specific example of the method in which a base station (cell)configures a SCell in consideration of the CSG registration situation ofthe user equipment is disclosed below. The cell can configure a cell(CC) that does not belong to a CSG as a SCell. The cell can configure,as a SCell, a cell (CC) operating in an open access mode or a cell (CC)operating in a hybrid access mode among the cells (CCs) belonging to theCSG. The cell can configure, as a SCell, a cell (CC) belonging to thesame CSG as a CSG with which the user equipment has been registeredamong the cells (CCs) belonging to the CSG. The cell cannot configure,as a SCell, a cell (CC) that operates in a closed access mode andbelongs to the CSG with which the user equipment has been unregisteredamong the cells (CCs) belonging to the CSG.

In a case of configuring, as a SCell, a cell (CC) operating in a hybridaccess mode among the cells (CCs) belonging to the CSG, the base station(cell) may perform as follows. The base station (cell) can configure, asa SCell, the cell (CC) for a user equipment registered with the CSG towhich the cell belongs in preference to a user equipment unregisteredwith the CSG.

The following three (1) to (3) are disclosed as specific examples of themethod in which a PCell knows whether or not another cell belongs to theCSG, an operation mode in a case where another cell belongs to the CSG,and a CSG-ID in a case where another cell belongs to the CSG.

(1) A PCell selects a SCell candidate cell before determining toconfigure a cell as a SCell. The PCell inquires the SCell candidate cellabout whether or not the SCell candidate cell belongs to the CSG, aCSG-ID to which the SCell candidate cell belongs, and an operation modeof the SCell candidate cell.

The PCell may inquire about “CSG indication” and “CSG-ID”. In that case,in a case where a response from the SCell does not contain a CSG-ID andthe CSG indication is “FALSE”, the PCell may judge that the SCell doesnot belong to the CSG or that the SCell belongs to the CSG and operatesin an open access mode. In a case where a response from the SCellcontains a CSG-ID and the CSG indication is “TRUE”, the PCell may judgethat the SCell belongs to the CSG and operates in a closed access mode.In a case where a response from the SCell contains a CSG-ID and the CSGindication is “FALSE”, the PCell may judge that the SCell belongs to theCSG and operates in a hybrid access mode.

The PCell may select a SCell candidate cell set before determining toconfigure a cell as a SCell. In this case, the PCell may inquire theSCell candidate cell set about the above.

(2) Each cell notifies the control unit of the base station of “whetheror not the own cell belongs to a CSG”, “CSG-ID” in a case where the owncell belongs to the CSG, and “operation mode” in a case where the owncell belongs to the CSG. The PCell selects a SCell candidate cell beforedetermining to configure a cell as a SCell. The PCell inquires thecontrol unit about whether or not a SCell candidate cell belongs to theCSG, a CSG-ID to which the SCell candidate cell belongs, and anoperation mode. The PCell may inquire about “CSG indication” and“CSG-ID”. The information shown by the combination of “CSG indication”and “CSG-ID” is similar to that of the specific example (1) describedabove. The PCell may select a SCell candidate cell set beforedetermining to configure a cell as a SCell. In this case, the PCell mayinquire the SCell candidate cell set about the above.

(3) Each cell notifies another cell of “whether or not the own cellbelongs to a CSG”, “CSG-ID” in a case where the own cell belongs to theCSG″, and “operation mode” in a case where the own cell belongs to theCSG. Each cell may notify “CSG indication” and “CSG-ID”. The informationshown by the combination of “CSG indication” and “CSG-ID” is similar tothat of the specific example (1) described above.

“Whether or not belonging to a CSG” in the specific examples (1) to (3)described above may be “indication of belonging to the CSG” or“indication of not belonging to the CSG”.

A specific example of the timing at which “whether or not belonging tothe CSG”, “CSG-ID”, and “operation mode” are notified is similar to thespecific example of the timing at which “SCell use configuration” isnotified in the first modification of the second embodiment describedabove, which is not described here.

The following two (1) and (2) are disclosed as specific examples of themethod in which a base station (cell) knows a CSG registration situationof a user equipment.

(1) A base station (cell) knows a CSG registration situation of a userequipment via an MME. The MME may notify the cell of the CSGregistration situation of the user equipment during a telephone call,during communication, or during CONNECTED via the cell. Thisnotification may be a registration situation of the user equipment withone or a plurality of CSGs to which a base station providing cellsbelongs. As a result, the cell does not notify the information not to beused in selection of a SCell, leading to an effect that communicationresources can be used effectively. The following two (a1) and (a2) aredisclosed as specific examples of a trigger to the notification.

(a1) The MME makes a notification spontaneously. (a2) The MME makes anotification, triggered by a request to the MME by a cell. The cell maymake the request in determination of a SCell candidate cell.Alternatively, the cell may request a notification of a registrationsituation of the user equipment with the CSG to which the SCellcandidate cell belongs. It suffices that in that case, the MME notifiesthe registration situation of the user equipment with the CSG to whichthe SCell candidate cell belongs.

(2) The base station (cell) knows a CSG registration situation of a userequipment via a UE. The user equipment during a telephone call, duringcommunication, or during CONNECTED may notify a cell of the CSGregistration situation of the user equipment. The following two (b1) and(b2) are disclosed as specific examples of the trigger to thenotification.

(b1) The user equipment makes a notification spontaneously. (b2) Theuser equipment makes a notification, triggered by a request to the userequipment by a cell. The cell may request a notification of aregistration situation of the user equipment with one or a plurality ofCSGs to which the base station providing the cell belongs. It sufficesthat in that case, the user equipment notifies a registration situationof the user equipment with one or a plurality of CSGs to which the basestation providing the cell belongs. As a result, the information not tobe used in selection of a SCell is not notified in the cell, leading toan effect that radio resources can be used effectively. Alternatively,the cell may make the request in determining a SCell candidate cell.Still alternatively, the cell may request the notification of theregistration situation of the user equipment with the CSG to which aSCell candidate cell belongs. It suffices that in that case, the userequipment notifies the registration situation of the user equipment withthe CSG to which the SCell candidate cell belongs.

Disclosed below is a specific example of the method in which a basestation (cell) knows a CSG registration situation of a user equipmentvia an MME. “UE Context” is used. “INITIAL CONTEXT SETUP REQUEST” thatis “UE Context” setup request to be notified a base station from an MMEor “UE context modification”, which is disclosed in Non-Patent Document11, may be used. This method is effective in that signaling does notneed to be newly provided, which enables to prevent a communicationsystem from becoming complex.

“CSG membership Status” included in “INITIAL CONTEXT SETUP REQUEST” maybe used for notifying the registration situation of the user equipment.This does not require additional parameters and enables to construct acommunication system having excellent backward compatibility.Alternatively, “CSG membership Status” may be newly provided in “UEcontext modification”. As a result, the base station (cell) can know aCSG registration situation of a user equipment via an MME when “UEContext” is changed other than when a user equipment first startscommunication with the base station (cell). Therefore, an effect that aflexible communication system can be constructed can be achieved.

The following three (1) to (3) are disclosed as specific examples ofchanges required to be made to the existing parameters. “INITIAL CONTEXTSETUP REQUEST” is described here for the sake of convenience, which alsoholds true for “UE context modification.

(1) In the conventional technique, in a case where a user equipment isaccessed via a cell operating in a hybrid access mode, “CSG membershipStatus” being the existing parameter is contained in “INITIAL CONTEXTSETUP REQUEST”. For this reason, in the conventional technique, in acase where a user equipment is accessed via a cell that does not belongto a CSG, via a cell operating in an open access mode among the cellsbelonging to the CSG, or via a cell operating in a closed access modeamong the cells belonging to the CSG, the MME cannot notify the cell ofthe registration situation of the user equipment.

Therefore, “INITIAL CONTEXT SETUP REQUEST” contains “CSG membershipStatus” in all cases irrespective of a cell via which a user equipmentis accessed. This enables the MME to notify the cell of the registrationsituation of the user equipment even in a case where a user equipment isaccessed via a cell that does not belong to a CSG, via a cell operatingin an open access mode among the cells belonging to the CSG, or via acell operating in a closed access mode among the cells belonging to theCSG.

A parameter different from “CSG membership Status” may be newlyprovided. Alternatively, “INITIAL CONTEXT SETUP REQUEST” may contain“CSG membership Status” in a case where a user equipment is accessed viaa cell capable of carrier aggregation. This results in that the celldoes not notify the information not to be used in selection of a SCell,leading to an effect that communication resources can be usedeffectively.

(2) In the conventional technique, “CSG membership Status” is notified acell via which a user equipment makes access. Therefore, in theconventional technique, an MME cannot notify a cell of the CSGregistration situation of a user equipment other than the CSG to whichthe cell belongs.

Therefore, “CSG membership Status” of “INITIAL CONTEXT SETUP REQUEST”may contain registration situations of all CSG-IDs with which a UE isregistered irrespective of a cell via which the user equipment makesaccess. This enables to notify a registration situation of a userequipment with a CSG other than a CSG to which a cell via which accessis made belongs. A parameter different from “CSG membership Status” maybe provided.

Alternatively, a registration situation of a user equipment regarding aCSG, to which another cell of the base station providing a cell viawhich the user equipment makes access belongs, may be notified. Thisresults in that the cell does not notify the information not to be usedin selection of a SCell, leading to an effect that communicationresources can be used effectively.

(3) Combination of (1) and (2) above.

A specific example of the operation of the MME is disclosed below. TheMME omits CSG access restriction, assuming that a PCell performs accesscontrol for a user equipment via a cell configured as a SCell by a basestation. The MME may only perform access control for a user equipmentvia a PCell. The MME may only perform access control for a userequipment via a PCell belonging to a CSG. The MME may only performaccess control for a user equipment via a PCell being a CSG cell.

A specific example of the operation of a user equipment is disclosedbelow. The user equipment omits CSG access control in a user equipment,assuming that the cell notified of the configuration content as a SCellis a cell accessible to the own user equipment. A specific example ofthe method in which a user equipment omits CSG access restriction issimilar to that of the third embodiment described above, which is notdescribed here.

Next, a specific example of a sequence of a communication system in thesixth embodiment is described with reference to FIG. 22. FIG. 22 is adiagram showing an example of the sequence of the communication systemin the sixth embodiment. The processes of Steps ST1401 to ST1416 of FIG.14 in the sixth embodiment are similar to those of the secondembodiment, which are not illustrated and described here. Illustrationand description are given from the process of Step ST1417 of FIG. 14.The sequence shown in FIG. 22 is similar to the sequences shown in FIGS.14, 15, and 19, where the same steps are denoted by the same stepnumbers and common description is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell1 of the base station A as thebest cell and camps on the cell to start communication, and thereafter,the cell2 is configured as a SCell. A case in which each cell notifiesthe control unit of the base station of “CSG indication” and “CSG-ID” ofthe own cell is disclosed as a specific example of the method in which aPCell knows whether or not another cell belongs to a CSG, a CSG-ID in acase where another cell belongs to the CSG, and an operation mode in acase where another cell belongs to the CSG. A case of the time when abase station is installed is disclosed as a specific example of thetiming at which “CSG indication” and “CSG-ID” are notified. A case inwhich a base station (cell) knows a CSG registration situation of a userequipment via an MME is disclosed as a specific example of the method inwhich the base station (cell) knows a CSG registration situation of auser equipment. Additionally, a case in which “INITIAL CONTEXT SETUPREQUEST” is used is disclosed as a specific example of the notificationmethod in a case where a base station (cell) knows a CSG registrationsituation of a user equipment via an MME.

The processes of Step ST1501 shown in FIG. 15 and Steps ST1901 andST1902 shown in FIG. 19 described above are performed, and then, theprocesses of Steps ST1401 to T1407 shown in FIG. 14 described above areperformed, so that the user equipment (UE) selects the cell1 of the basestation A as the best cell and camps on the cell1.

In Step ST2201, the MME requests “UE Context” setup of the userequipment from the base station (cell). The MME may request “UE Context”setup of the user equipment from a PCell. Alternatively, the MME maynotify the base station (cell) of the CSG registration situation of theuser equipment. “INITIAL CONTEXT SETUP REQUEST” may be used as thisrequest. “INITIAL CONTEXT SETUP REQUEST” may contain “CSG MembershipStatus”.

Then, the processes of Steps ST1408 to ST1416 shown in FIG. 14 describedabove are performed, and then, in Step ST1417, the cell being a PCellstarts communication with the user equipment (UE). In this operationexample, the cell1 starts communication with the user equipment as aPCell.

Then, the processes of Steps ST1504 and ST1903 to Step ST1905 areperformed, and then, in Step ST1906, the cell being a PCell judgeswhether or not the CSG indication of the cell being a SCell candidateselected in Step ST1504 is “TRUE”. In other words, the cell being aPCell judges whether or not the access mode of the SCell is a closedaccess mode. The response results to the inquiry received from thecontrol unit in Step ST1904 are used in this judgment.

In a case of judging that the CSG indication of the cell being a SCellcandidate selected in Step ST1504 is not “TRUE”, that is, is “FALSE” inStep ST1906, the cell being a PCell moves to Step ST1508. In otherwords, in a case of judging that the operation mode of the cell being aSCell candidate selected in Step ST1504 is an open access mode or hybridaccess mode in Step ST1906, the cell being a PCell moves to Step ST1508.

In a case of judging that the CSG indication of the SCell candidateselected in Step ST1504 is “TRUE” in Step ST1906, the cell being a PCellmoves to Step ST2202. In other words, in a case of judging that theoperation mode of the cell being a SCell candidate selected in StepST1504 is a closed access mode in Step ST1906, the cell being a PCellmoves to Step ST2202.

In Step ST2202, the cell being a PCell judges whether or not the userequipment has been registered with a CSG to which the cell being a SCellcandidate selected in Step ST1504 belongs. The response results to theinquiry received from the control unit in Step ST1904 are used for theCSG to which the cell being a SCell candidate belongs in this judgment.Alternatively, the notification received from the MME in Step ST2201 isused for the CSG registration situation of the user equipment in thisjudgment.

In a case of judging that the user equipment has been registered withthe CSG to which the cell being a SCell candidate belongs in StepST2202, the cell being a PCell moves to Step ST1508. In a case ofjudging that the user equipment has been unregistered with the CSG towhich the cell being a SCell candidate has been unregistered in StepST2202, the cell being a PCell returns to Step ST1504 to select anothercell as a cell being a SCell candidate.

Through the processes of Steps ST1905, ST1906, and ST2202, a cell (CC)that does not belong to a CSG, a cell (CC) operating in an open accessmode among the cells (CCs) belonging to the CSG, a cell (CC) operatingin a hybrid access mode among the cells (CCs) belonging to the CSG, or acell (CC) belonging to the same CSG as that of the CSG with which theuser equipment has been registered among the cells (CCs) belonging tothe CSG can be configured as a SCell, which is specific to the presentembodiment. Alternatively, among the cells (CCs) belonging to the CSG, acell (CC) that operates in a closed access mode and belongs to a CSGwith which the user equipment has been unregistered cannot be configuredas a SCell.

The sixth embodiment described above can achieve the following effects.As in the third embodiment described above, subscribers who are allowedto use the SCell can be specified by an operator. The SCell belongs tothe CSG, whereby a user-friendly communication system can beconstructed, in which wishes of users are taken into consideration, suchas services that users want to receive or charging setting that userswant to apply for. At the same time, as in the second embodimentdescribed above, the operation as a communication system can bestabilized while improving a data rate using carrier aggregation, whichenables to appropriately provide services.

The present embodiment can be used in combination with the firstembodiment described above.

Seventh Embodiment

A seventh embodiment discloses another solution to the same problem asthat of the second embodiment described above. The solution in theseventh embodiment is described below. Each cell (CC) is not allowed toconfigure a CSG-ID per cell (CC). One or a plurality of cells (CCs)provided by the same base station belong to one CSG. In a base stationcapable of carrier aggregation, each cell (CC) may not be allowed toconfigure a CSG-ID per cell (CC). One or a plurality of cells (CCs)provided by a base station capable of carrier aggregation may belong toone CSG.

A specific example of the operation of the MME is disclosed below. TheMME omits access control for a user equipment via a cell configured as aSCell by a base station, as in the case of the access control for a userequipment via a PCell. The MME may only perform access control for auser equipment via a PCell. The MME may only perform access control fora user equipment via a PCell belonging to a CSG. The MME may onlyperform access control for a user equipment via a PCell being a CSGcell.

The following two (1) and (2) are disclosed as specific examples of theoperation of the base station.

(1) A base station is allowed to configure any cell of the base stationas a SCell in a case of performing carrier aggregation. Additionally, ina case of performing carrier aggregation, the base station is allowed toconfigure any cell as a SCell even in a case where a cell belonging tothe CSG is provided by the base station.

(2) A base station is allowed to render any cell of the base stationactive as a SCell in a case of performing carrier aggregation.Additionally, in a case of performing carrier aggregation, the basestation is allowed to render any cell active as a SCell even in a casewhere a cell belonging to the CSG is provided by the base station.

In configuring a cell as a SCell, a cell (PCell) may not notify a userequipment of the CSG-indication and CSG-ID of the SCell.

A specific example of the operation of the user equipment is disclosedbelow. The user equipment omits CSG access control, that is, CSG accessrestriction, on a cell whose configuration content has been notified asa SCell, as in the case of the access control of a PCell. A specificexample of the method in which a user equipment omits CSG accessrestriction is similar to that of the third embodiment described above,which is not described here.

A specific example of the sequence of the communication system in theseventh embodiment is similar to the sequence shown in FIG. 14, which isnot described here.

The seventh embodiment described above can achieve the followingeffects. As in the third embodiment described above, subscribers who areallowed to use the SCell can be specified by an operator. The SCellbelongs to the CSG, whereby a user-friendly communication system can beconstructed, in which wishes of users are taken into consideration, suchas services that users want to receive or charging setting that userswant to apply for. At the same time, the operation as a communicationsystem can be stabilized while improving a data rate using carrieraggregation as in the second embodiment described above, which enablesto appropriately provide services.

In the seventh embodiment, control as a communication system can be mademore easily in a user equipment or base station compared with the thirdembodiment, fourth embodiment, fifth embodiment, and sixth embodimentdescribed above. Therefore, a more enhanced effect of preventing controldelays can be achieved compared with the third embodiment, fourthembodiment, fifth embodiment, and sixth embodiment.

Eighth Embodiment

Non-Patent Document 1 described above discloses that handovers in an LTEsystem include a handover via an X2 interface (also referred to as X2handover) and a handover via an S1 interface (also referred to as S1handover). It is also disclosed that the S1 handover is used in mobilityfrom an eNB or HeNB to a CSG cell or hybrid cell.

FIG. 23 is a diagram showing the sequence of the communication systemregarding the handover method from an eNB or HeNB to a CSG cell orhybrid cell, which is disclosed in Non-Patent Document 1.

In Step ST2300, a source eNB starts communication with a user equipment(UE). In Step ST2301, the source eNB notifies the user equipment of ameasurement configuration.

In Step ST2313, the user equipment performs a measurement report inaccordance with the measurement configuration notified in Step ST2301.The measurement report contains the PCI of a measurement target cell andthe like.

In Step ST2314, the source eNB reconfigures the measurementconfiguration of requesting the reception and report of the systeminformation of a measurement target cell as required. The source eNBconfigures a measurement gap as required. The measurement gap is aperiod in which data transmission/reception at a frequency at which theuser equipment currently receives services is stopped for measuringanother system or another frequency.

In Step ST2302, the user equipment performs a measurement report inaccordance with the measurement reconfiguration notified in Step ST2314.This measurement report contains the CSG-ID of the measurement targetcell and the member indication for the measurement target cell. Themember indication is a membership status that is judged based on theCSG-ID that the user equipment has received from the target cell and thewhitelist in the user equipment. The CSG-ID of the measurement targetcell and the like can be obtained when the user equipment receives thesystem information of the measurement target cell.

In Step ST2303, the source eNB determines handover (HO) in considerationof the measurement report received from the user equipment in StepST2302.

In Step ST2304, the source eNB notifies the MME of a handover request.The handover request is also referred to as handover required. Thehandover request contains the CSG-ID of the target cell determined inStep ST2303. In a case where the target cell is a hybrid cell, thehandover request contains an access mode of the target cell (Cell AccessMode).

In Step ST2305, the MME performs access control. Specifically, the MMEjudges whether or not the user equipment has been registered with theCSG-ID of the target cell received in Step ST2304, to thereby judgewhether or not the user equipment can access the target cell. The CSGsubscription data of the user equipment stored in the MME is used forjudging whether or not the user equipment has been registered with theCSG-ID of the target cell.

In Step ST2306, the MME judges whether or not handover is allowed inconsideration of the access control results of Step ST2305, that is, thejudgment results as to whether or not the user equipment can access atarget cell.

Specifically, in a case of judging that the user equipment cannot accessa target cell in Step ST2305, the MME judges that handover is notallowed in Step ST2306. In a case of judging that handover is notallowed in Step ST2306, the MME ends the process and moves to otherprocess. The other process is not specific to the present invention,which is not described here.

In a case of judging that the user equipment can access a target cell inST2305, the MME judges that handover is allowed in Step ST2306 and movesto Step ST2307.

In Step ST2307, the MME notifies a target eNB being a target cell of ahandover request. This handover request contains the CSG-ID of thetarget eNB received from the source eNB. In a case where the target eNBis a hybrid cell, the handover request contains a membership status.

In Step ST2308, the target eNB judges whether or not the CSG-IDcontained in the handover request received in Step ST2307 is identicalto the CSG-ID broadcast by the own eNB. Hereinafter, this judgment maybe referred to as “CSG-ID check”.

In Step ST2309, the target eNB judges whether or not the CSG-ID checkresults are OK, that is, are good using the judgment results of StepST2308. In a case of judging that the CSG-IDs are identical to eachother in Step ST2308, the target eNB judges that the CSG-ID checkresults are good in Step ST2309 and moves to Step ST2310. In a case ofjudging that the CSG-IDs are not identical to each other, that is, aredifferent from each other in Step ST2308, the target eNB judges that theCSG-ID check results are not good in Step ST2309, ends the process, andmoves to other process. The other process is not specific to the presentinvention, which is not described here.

In Step ST2310, the target eNB notifies the MME of handover requestacknowledge. In Step ST2311, the MME that has received the handoverrequest acknowledge from the target eNB in Step ST2310 notifies thesource eNB of a handover command. In Step ST2312, the source eNB thathas received the handover command from the MME in Step ST2311 notifiesthe user equipment of the handover command.

Non-Patent Document 1 describes that the PCell can only be changedthrough handover. However, Non-Patent Document 1 does not pose a problemregarding the relationship between a CSG to which a CC (cell) being ahandover destination belongs and a CSG to which a user equipment belongsand does not disclose a solution to the problem.

R2-104788 (hereinafter, referred to as “Non-Patent Document 12”) by 3GPPdiscloses that the PCell should be changed in reconfiguration. However,Non-Patent Document 12 does not pose a problem regarding therelationship between a CSG to which a CC (cell) being a handoverdestination belongs and a CSG to which a user equipment belongs and doesnot disclose a solution to the problem.

A problem to be solved in the eighth embodiment is described below. Theconventional technique does not disclose an appropriate access controlmethod in a change of a PCell to a CSG cell in the same base station(eNB) or a hybrid cell. Further, as to access from a user equipment viaa CSG cell, the MME performs access control as described above. That is,the base station does not perform CSG access restriction. Therefore, fora UE unregistered with a CSG to which a cell belongs, that cell (CC) maybe treated as a CC being a PCell change destination. This causes aproblem that services cannot be provided appropriately.

A solution in the eighth embodiment is described below. The MME performsaccess control of a CC being a PCell change destination (hereinafter,also referred to as “target CC”). The PCell (hereinafter, also referredto as “source CC”) notifies the MME of the CSG-ID of the target CC.

The source cell (PCell) may change the method of obtaining the CSG-ID ofthe target CC depending on whether or not the target cell is provided bythe same base station. Alternatively, the source cell (PCell) may changethe method of obtaining the CSG-ID of the target CC depending on whetheror not the target cell is controlled by the same control unit.

A specific example of the method in which the source cell judges whetheror not the target cell is provided by the same base station is disclosedbelow. The source cell makes a judgment based on the cell identificationinformation of a measurement target cell (target cell) contained in themeasurement report of the user equipment. Specific examples of the cellidentification information include PCI and GCI. In a case where a cellhaving the cell identification information of the measurement targetcell is provided by the same base station as that of the source cell,the source cell judges that the target cell is provided by the same basestation. In a case where a cell having the cell identificationinformation of the measurement target cell is not provided by the samebase station as that of the source cell, the source cell judges that thetarget cell is not provided by the same base station. The entity forjudgment in the source cell may be a source cell (PCell) or controlunit.

Disclosed below is a specific example of the method in which the PCellknows the CSG-ID of the target CC in a case where the target cell is notprovided by the same base station as that of the PCell (source CC). ThePCell obtains the CSG-ID from the measurement report of the userequipment. This specific example is also given as a specific example ofthe method in which the PCell knows the CSG-ID of the target CC in acase where the target cell is not controlled by the same control unit asthat of the PCell (source CC).

The following four (1) to (4) are disclosed as specific examples of themethod in which the PCell knows the CSG-ID of the target CC in a casewhere the target cell is provided by the same base station as that ofthe PCell (source CC). The specific examples (1) to (4) below can bealso given as specific examples of the method in which the PCell knowsthe CSG-ID of the target cell in a case where the target cell iscontrolled by the same control unit as that of the PCell (source CC).

(1) The PCell obtains the CSG-ID from the measurement report of the userequipment. This specific example is similar to the handover method froman eNB or HeNB to a CSG cell or hybrid cell, which is disclosed inNon-Patent Document 1. Therefore, this specific example can achieve aneffect that a communication system can be prevented from becomingcomplex differently from the specific examples (2) to (4) describedbelow.

(2) The PCell inquires the target CC about “CSG-ID”. As a result, thePCell needs not to obtain the CSG-ID of the measurement target cell(target CC) from the measurement report of the user equipment. Further,differently from the specific example (1), the user equipment needs notto receive the system information of the measurement target cell in thisspecific example. Therefore, it is not required to provide a measurementgap to a user equipment, leading to an effect that a reduction in datarate of a user equipment can be prevented.

(3) Each cell notifies the control unit of the base station of “CSG-ID”of the own cell. The PCell inquires the control unit about “CSG-ID” ofthe target CC. As a result, the PCell needs not to obtain the CSG-ID ofthe measurement target cell (target CC) from the measurement report ofthe user equipment. Further, differently from the specific example (1),the user equipment needs not to receive the system information of themeasurement target cell in this specific example. Therefore, it is notrequired to provide a measurement gap to a user equipment, leading to aneffect that a reduction in data rate of a user equipment can beprevented. Alternatively, the control unit may notify each cell (PCell)of “CSG-ID” of each cell before an inquiry from the PCell.

(4) Each cell notifies another cell of “CSG-ID” of the own cell. As aresult, the PCell needs not to obtain the CSG-ID of the measurementtarget cell (target CC) from the measurement report of the userequipment. Further, differently from the specific example (1), the userequipment needs not to receive the system information of the measurementtarget cell in this specific example. Therefore, it is not required toprovide a measurement gap to a user equipment, leading to an effect thata reduction in data rate of a user equipment can be prevented.

The specific examples (2) to (4) can be implemented easily because thePCell (source CC) and target CC are provided by the same base station.Alternatively, those examples can be implemented easily because thePCell (source CC) and target CC are controlled by the same control unit.

The following two (1) and (2) are disclosed as specific examples of themethod in which a source CC notifies the MME of the CSG-ID of the targetCC.

(1) S1 signaling is newly provided. A parameter to be mapped to thenewly provided S1 signaling is the CSG-ID of the target CC, which may benotified together with the user equipment identifier. The user equipmentidentifier may be UE-ID or IMSI.

(2) The existing S1 signaling is used. Specific examples of the existingsignaling include a handover request. The handover request is alsoreferred to as handover required. This specific example is similar tothe handover method from an eNB or HeNB to a CSG cell or hybrid cell,which is disclosed in Non-Patent Document 1. Therefore, this specificexample can achieve an effect that a communication system can beprevented from becoming complex.

The MME performs access control using the CSG-ID of the target CCreceived from the source CC.

Next, a specific example of a sequence of a communication system in theeighth embodiment is described with reference to FIG. 24. FIG. 24 is adiagram showing an example of the sequence of the communication systemin the eighth embodiment. The processes of Steps ST1401 to ST1416 ofFIG. 14 described above in the present embodiment are similar to thoseof the second embodiment, which are not illustrated and described here.The sequence shown in FIG. 24 is similar to the sequence shown in FIG.23, where the same steps are denoted by the same step numbers and commondescription is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell1 of the base station A as thebest cell and camps on the cell to start communication, and thereafter,the cell2 is configured as a CC being a PCell change destination. A casein which each cell notifies the control unit of the base station of“CSG-ID” of the own cell is disclosed as a specific example of themethod in which a PCell knows the CSG-ID of the target CC.

In Step ST2400, a base station is installed. In this operation example,the base station A providing a plurality of cells (CCs) including thecell and cell2 is installed. In Steps ST2401 and ST2402, each cell ofthe base station notifies the control unit of the base station of theconfiguration of the own cell. The configuration of the own cellcontains “CSG-ID”. In this operation example, in Step ST2401, the cell1notifies the control unit of “CSG-ID” of the cell1. In Step ST2402, thecell2 notifies the control unit of “CSG-ID” of the cell2.

Then, the processes of Steps ST1401 to ST1416 shown in FIG. 14 describedabove are performed, and then, in Step ST2300, the source CC being asource eNB starts communication with a user equipment (UE). In thisoperation example, the cell starts communication with the user equipment(UE) as the source CC being a source cell (PCell).

In Step ST2403, the source CC (cell1) notifies the user equipment (UE)of the measurement configuration. In Step ST2404, the user equipment(UE) performs a measurement report to the source CC (cell1) inaccordance with the measurement configuration notified in Step ST2403.The measurement report contains, for example, the PCI of the measurementtarget cell.

In Step ST2303, the source CC (cell1) being a source eNB determineshandover in consideration of the measurement report received from theuser equipment (UE) in Step ST2404. Alternatively, the source CC (cell1)being a source cell (PCell) may judge whether or not the target cell isprovided by the same base station and determine the method of obtainingthe CSG-ID of the target CC. In this operation example, the source CC(cell1) judges that the target CC (cell2) is provided by the same basestation.

In this operation example, the method in which each cell notifies thecontrol unit of the base station of “CSG-ID” of the own cell is selectedas the method of obtaining the CSG-ID of the target CC. In this case,the source CC does not reconfigure, for the user equipment (UE), themeasurement configuration of requesting the reception and report of thesystem information of the measurement target cell in Step ST2314 of FIG.23. As a result, the user equipment needs not to receive the systeminformation of the measurement target cell. Therefore, it is notrequired to provide a measurement gap to the user equipment, leading toan effect that a reduction in data rate of the user equipment can beprevented. This is because the PCell obtains the CSG-ID of the target CCfrom the control unit or the like. The method of obtaining the CSG-IDmay be determined independently of the handover determination.

In Step ST2405, the cell inquires the control unit about theconfiguration of the target CC determined in Step ST2303. The cell mayinquire the control unit about “CSG-ID” and “access mode” of the targetCC. In this operation example, the cell being a PCell inquires thecontrol unit about “CSG-ID” and “access mode” of the cell2 selected asthe target CC. The cell may inquire about “CSG-ID” and “CSG indication”in place of inquiring about “CSG-ID” and “access mode”.

In Step ST2406, the control unit responds to the inquiry from the cellin Step ST2405. The control unit may notify the cell of “CSG-ID” and“access mode” of the inquiry target cell. In this operation example, thecontrol unit notifies the cell being a PCell of “CSG-ID” and “accessmode” of the cell2 being an inquiry target cell. The control unit maynotify “CSG-ID” and “CSG indication” in place of notifying “CSG-ID” and“access mode”.

In Step ST2407, the PCell notifies the MME of a handover request. Thehandover request is also referred to as handover required. The handoverrequest contains the CSG-ID of the target CC determined in Step ST2303.The handover request may contain an access mode of the target CC (cellaccess mode).

In Step ST2305, the MME performs access control. Specifically, the MMEjudges whether or not the user equipment has been registered with theCSG-ID of the target CC received in Step ST2407, to thereby judgewhether or not the user equipment can access the target CC. The CSGsubscription data of the user equipment stored in the MME is used injudging whether or not the user equipment has been registered with theCSG-ID of the target CC. The HSS may be inquired about the CSGsubscription data of the user equipment, or the information stored inthe HSS may be used as the CSG subscription data of the user equipment.Access control may include, for example, the processes of Steps ST1411to ST1414 shown in FIG. 14 described above.

In Step ST2306, the MME judges whether or not handover is allowed inconsideration of the results of access control in Step ST2305 asdescribed above. The MME moves to Step ST2408 in a case of judging thathandover is allowed or ends the process and moves to other process in acase of judging that handover is not allowed.

In Step ST2408, the MME notifies the cell2 being a target CC of ahandover request. The handover request contains the CSG-ID of the targetCC being a target eNB received from the source CC being a source eNB.This handover request may contain a membership status. With the use ofthe handover request, the method is similar to the handover method froman eNB or HeNB to a CSG cell or hybrid cell, which is disclosed inNon-Patent Document 1 described above. This achieves an effect that acommunication system can be prevented from becoming complex.

In Step ST2409, the cell2 being a target CC checks the CSG-ID.Specifically, the cell2 being a target CC judges whether or not theCSG-ID contained in the handover request received in Step ST2408 and theCSG-ID broadcast by the own eNB are identical to each other.Alternatively, the cell2 may judge whether or not handover can beaccepted (hereinafter, also referred to as “judgment as to whether ornot handover can be accepted” or “check of the acceptance of handover).Still alternatively, the cell2 may perform both of the CSG-ID check andthe judgment as to whether or not handover can be accepted.

In Step ST2410, the cell2 being a target CC checks whether or not theCSG-ID check results are OK, that is, are good, using the judgmentresults of Step ST2409. In a case of judging that the CSG-IDs areidentical to each other in Step ST2409, the cell2 being a target CCjudges that the CSG-ID check results are good in Step ST2410, and thenmoves to Step ST2310. In a case of judging that the CSG-IDs aredifferent from each other in Step ST2409, the cell2 being a target CCjudges that the CSG-ID check results are not good in Step ST2410. Then,the cell2 ends the process and moves to other process. The other processis not specific to the present invention, which is not described here

In judging whether or not handover can be accepted in Step ST2409, inStep ST2410, the cell2 being a target CC judges whether or not thejudgment results as to whether or not handover can be accepted are OK,that is, whether or not handover can be accepted. In a case ofperforming both of the CSG-ID check and the judgment as to whether ornot handover can be accepted in Step ST2409, in Step ST2410, the cell2being a target CC judges whether or not the CSG-ID check results and thejudgment results as to whether or not handover can be accepted are OK,that is, are good. The cell2 moves to Step ST2310 in a case of judgingthat the results are good in Step ST2410, or ends the process and movesto other process in a case of judging that the results are not good.

In Step ST2310, the cell2 being a target CC notifies the MME of handoverrequest acknowledge. In Step ST2311, the MME that has received thehandover request acknowledge from the cell2 in Step ST2310 notifies thecell1 being a source CC of a handover command. In Step ST2312, the cell1that has received the handover command from the MME in Step ST2311notifies the user equipment (UE) of the handover command.

The eighth embodiment described above can achieve the following effects.The operation as a communication system can be stabilized whileimproving a data rate using carrier aggregation, which enables toappropriately provide services. Additionally, it is not required toprovide a measurement gap to the user equipment, which enables toprevent a reduction in data rate of the user equipment.

While the present embodiment has mainly described the case in whichhandover is used in changing a PCell, the present embodiment is alsoapplicable to the case in which a reconfiguration is used in changing aPCell.

The present embodiment can be used in combination with the firstembodiment, second embodiment, first modification of the secondembodiment, third embodiment, fourth embodiment, fifth embodiment, firstmodification of the fifth embodiment, sixth embodiment, and seventhembodiment described above.

First Modification of Eighth Embodiment

A first modification of the eighth embodiment discloses another solutionto the same problem as that of the eighth embodiment described above.The present modification mainly describes a portion different from thesolution in the eighth embodiment described above, and a portion not tobe described is similar to the eighth embodiment.

In a case where a target cell is provided by the same base station, thesource cell (PCell) can omit “judgment as to whether or not handover canbe accepted” or “check of CSG-ID” in the target cell (CC). For example,in Step ST2409 of FIG. 24, “judgment as to whether or not handover canbe accepted” or “check of CSG-ID” can be omitted. Signaling required for“judgment as to whether or not handover can be accepted” or “check ofCSG-ID” can be omitted.

Alternatively, both of “judgment as to whether or not handover can beaccepted” and “check of CSG-ID” can be omitted. Still alternatively,“judgment as to whether or not handover can be accepted” or “check ofCSG-ID” in the target cell may be performed by the source cell (CC).Specific examples of the case in which the source cell (PCell) isprovided by the base station as that of the target cell include the casein which the PCell is changed.

The following effects can be achieved through the above. Control delaysin a communication system can be prevented. In addition, the processingload of the base station can be reduced. Further, power consumption ofthe base station can be reduced.

The omission described above can be made easily in a case where thePCell (source CC) and target CC are provided by the same base station.Alternatively, the omission described above can be made easily in a casewhere the PCell (source CC) and target CC are controlled by the samecontrol unit.

A specific example of the method in which a source cell determineswhether or not the target cell is provided by the same base station issimilar to that of the eighth embodiment, which is not described here.

The following four (1) to (4) are disclosed as specific examples of theprocess (hereinafter, also referred to as “control step”) such as thejudgment that may be omitted and signaling.

(1) Notification of handover request acknowledge from the target CC tothe MME, which is, for example, the process of Step ST2310 in FIG. 24.In a case of notifying the MME of the CSG-ID of the target CC, the PCellmay notify that a response from the target CC to the MME is omitted. Forexample, in Step ST2407 of FIG. 24, the PCell may notify that a responsefrom the target CC to the MME is omitted. This notification may be aninformation element of a message by which the source CC being a PCellnotifies the MME of the CSG-ID of the target CC. This notification maybe replaced by the indication showing a PCell change. According to thisspecific example, the MME can judge explicitly whether or not a responseto a handover request is present after the notification of the handoverrequest. This leads to an effect that a stable communication system canbe constructed.

(2) Notification of a handover command from the MME to the PCell being asource CC, which is, for example, the process of Step ST2311 in FIG. 24.A message by which the source CC can recognize that handover is allowedby the MME may be provided. Specific examples of the new message includea notification from a target CC that has received a handover requestfrom the MME. Specific examples of the notification include handoverrequest acknowledge.

(3) Judgment as to whether or not the CSG-ID contained in a handoverrequest at a target CC and the CSG-ID broadcast by the own eNB areidentical to each other, that is, “check of CSG-ID”. Or, “judgment as towhether or not handover can be accepted”, or both of “judgment as towhether or not handover can be accepted” and “check of CSG-ID”. Forexample, any one or both of the processes of Steps ST2409 and ST2410 ofFIG. 24.

The specific example (3) is effective particularly in a case where thespecific examples (2) to (4) of the method in which a PCell knows theCSG-ID of a target CC. This is because it is not required to obtain theCSG-ID from a user equipment, with few problems such as a communicationerror.

In a case where the judgment described above is omitted, thenotification of a handover request from the MME to the target CC may beomitted. For example, the process of Step ST2408 of FIG. 24 may beomitted. A handover command or handover request from the MME to thesource CC may be notified. The handover command or handover request maycontain a membership status. In a case of notifying the MME of theCSG-ID of a target CC, the PCell may notify that the target CC omits theabove-mentioned judgment. Alternatively, the PCell may notify that thesource CC performs the above-mentioned judgment. This notification maybe an information element of a message by which the PCell notifies theMME of the CSG-ID of the target CC. This notification may be replaced bya PCell change.

According to the specific example (3), the MME can explicitly judge adestination to be notified of a handover request. This leads to aneffect that a stable communication system can be constructed.

In a case where the source cell (CC) performs “judgment as to whether ornot handover can be accepted” by a target cell in the specific example(3), the situations regarding the processing load and resource use of atarget CC may be taken into consideration. The following is disclosed asa specific example of the method in which a PCell being a source cellknows the situations regarding the processing load and resource use ofanother cell. The situations regarding the processing load, resourceuse, and the like may be contained in the configuration of the own cell.

(4) Combination of (1) to (3) above.

The specific examples (2) to (4) can be performed easily in a case wherethe source CC being a PCell and the target CC are provided by the samebase station. Alternatively, those examples can be performed easily in acase where the source CC being a PCell and the target CC are controlledby the same control unit.

Next, a specific example of a sequence of a communication system in thefirst modification of the eight embodiment is described with referenceto FIG. 25. FIG. 25 is a diagram showing an example of the sequence ofthe communication system in the first modification of the eighthembodiment. The processes of Steps ST1401 to ST1416 of FIG. 14 describedabove in the present embodiment are similar to those of the secondembodiment, which are not illustrated and described here. The sequenceshown in FIG. 25 is similar to the sequences shown in FIGS. 23 and 24,where the same steps are denoted by the same step numbers and commondescription is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell1 of the base station A as thebest cell and camps on the cell to start communication, and thereafter,the cell2 is configured as a CC being a PCell change destination. A casein which each cell notifies the control unit of the base station of“CSG-ID” of the own cell is disclosed as a specific example of themethod in which the PCell knows the CSG-ID of the target CC. As specificexamples of the control step that can be omitted, the following casesare disclosed: notification of handover request acknowledge from thetarget CC to the MME in the specific example (1) described above;notification of a handover command from the MME to the PCell being asource CC in the specific example described (2) above; check of CSG-IDat the target CC, that is, judgment as to whether or not the CSG-IDcontained in the handover request and the CSG-ID broadcast by the owneNB are identical to each other, in the specific example (3) describedabove; and judgment as to whether or not handover can be accepted.

After the processes of Steps ST2400 to ST2402 are performed as describedabove, the processes of Steps ST1401 to ST1416 shown in FIG. 14described above are performed, and then, the processes of Steps ST2300,ST2403, ST2404, ST2303, ST2405, and ST2406 are performed in order.

Then, in Step ST2501, the cell being a PCell notifies the MME of ahandover request. The handover request is also referred to as handoverrequired. The handover request contains the CSG-ID of the target CCdetermined in Step ST2303. The handover request may contain an accessmode of the target CC (cell access mode). Alternatively, the handoverrequest may contain a PCell change.

In this operation example, a PCell change is indicated, so that it isnotified that the notification of the handover request acknowledge fromthe target CC to the MME is omitted and that the judgment as to whetheror not the CSG-ID contained in the handover request at the target CC andthe CSG-ID broadcast by the own eNB are identical to each other, thatis, check of CSG-ID, is omitted. In a case where the source CC being aPCell performs “judgment as to whether or not handover can be accepted”or “check of CSG-ID”, which may be performed prior to, for example, StepST2501. The configuration information of the target CC received in StepST2406 may be used for the “judgment as to whether or not handover canbe accepted” or “check of CSG-ID”.

Then, the processes of Steps ST2305 and ST2306 are performed. Then, inStep ST2502, the MME notifies the cell1 being a source CC of thehandover request or handover command. Upon receipt of the indicationshowing a PCell change in Step ST2501, the MME may change a destinationto be notified of the handover request from the target CC to the sourceCC.

The first modification of the eighth embodiment described above canachieve the following effects in addition to the effects of the eighthembodiment. The control steps are omitted in the present modification,whereby control delays in the communication system can be prevented. Inaddition, the processing load of the base station can be reduced.Further, power consumption of the base station can be reduced.

While the present modification has mainly described the case in whichhandover is used in PCell change, the present modification is alsoapplicable to the case in which a reconfiguration is used in PCellchange.

The present modification can be used in combination with the firstembodiment, second embodiment, first modification of the secondembodiment, third embodiment, fourth embodiment, fifth embodiment, firstmodification of the fifth embodiment, sixth embodiment, seventhembodiment, and eighth embodiment described above.

Second Modification of Eighth Embodiment

A second modification of the eighth embodiment describes anothersolution to the same problem as that of the eighth embodiment. Asolution in the second modification of the eighth embodiment isdescribed below. The present modification mainly describes a portiondifferent from the solution in the eighth embodiment, and a portion notto be described is similar to the eighth embodiment. In the presentmodification, the base station performs access control on the target CC,which may be performed by a PCell.

The PCell being a source cell may change the access control method for atarget CC depending on whether or not the target cell is provided by thesame base station. Alternatively, the PCell being a source cell maychange the access control method for a target CC depending on whether ornot the target cell is controlled by the same control unit.

A specific example of the method in which a source cell judges whetheror not the target cell is provided by the same base station is similarto that of the eighth embodiment, which is not described here.

Disclosed below is a specific example of the access control method for atarget CC in a case where the target cell is not provided by the samebase station as that of the source CC being a PCell. For example, asshown in FIG. 23 described above, the MME performs access control on thetarget CC. This specific example is also given as a specific example ofan access control method for a target CC in a case where the target cellis not controlled by the same control unit as that of the source CCbeing a PCell.

Disclosed below is a specific example of the access control method for atarget CC in a case where the target cell is provided by the same basestation as that of the source CC being a PCell. The specific exampledisclosed below is also given as a specific example of an access controlmethod for a target CC in a case where the target cell is controlled bythe same control unit as that of the source CC being a PCell.

The cell is allowed to configure or select, as a target CC, a cell (CC)that does not belong to a CSG. The cell is allowed to configure orselect, as a target CC, a cell (CC) operating in an open access mode ora cell (CC) operating in a hybrid access mode among the cells (CCs)belonging to the CSG. The cell is allowed to configure or select, as atarget CC, a cell (CC) belonging to the same CSG as the CSG with whichthe user equipment has been registered among the cells (CCs) belongingto the CSG. The cell is not allowed to configure or select, as a targetCC, a cell (CC) that operates in a closed access mode and belongs to aCSG with which a user equipment has been unregistered among the cells(CCs) belonging to the CSG.

The base station (cell) may perform as follows in a case of configuringor selecting, as a target CC, a cell (CC) operating in a hybrid accessmode among the cells (CCs) belonging to the CSG. The base station isallowed to configure or select, as a target CC, a cell (CC) for a userequipment registered with a CSG to which the cell belongs in preferenceto a user equipment unregistered therewith.

A specific example of the method in which a PCell knows whether or notanother cell belongs to a CSG and knows the operation mode and CSG-ID ina case where another cell belongs to the CSG is similar to that of thesixth embodiment, which is not described here.

A specific example of the method in which a base station (cell) knows aCSG registration situation of a user equipment is similar to that of thesixth embodiment, which is not described here.

Next, a specific example of a sequence of a communication system in thesecond modification of the eighth embodiment is described with referenceto FIG. 26. FIG. 26 is a diagram showing an example of the sequence ofthe communication system in the second modification of the eighthembodiment. The processes of Steps ST1401 to ST1416 of FIG. 14 describedabove in the present modification are similar to those of the secondembodiment, which are not illustrated and described here. The sequenceshown in FIG. 26 is similar to the sequences shown in FIGS. 23 and 24,where the same steps are denoted by the same step numbers and commondescription is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell of the base station A as the bestcell and camps on the cell to start communication, and thereafter, thecell2 is configured as a CC being a PCell change destination. A case inwhich each cell notifies the control unit of the base station of“CSG-ID” of the own cell is disclosed as a specific example of themethod in which a PCell knows the CSG-ID of the target CC. A case inwhich a base station (cell) knows a CSG registration situation of a userequipment via an MME is disclosed as a specific example of the method inwhich the base station knows the CSG registration situation of the userequipment. Also, a case in which “INITIAL CONTEXT SETUP REQUEST” is usedis disclosed as a specific example of the notification method in a casewhere a base station (cell) knows the CSG registration situation of theuser equipment via the MME.

The processes of Steps ST2400 to ST2402 are performed, and thereafter,the processes of Steps ST1401 to T1407 shown in FIG. 14 described aboveare performed, so that the user equipment (UE) selects the cell of thebase station A as the best cell and camps on the cell1.

In Step ST2601, the MME requests “UE Context” setup of the userequipment from a base station (cell). The MME may request “UE Context”setup of the user equipment from a PCell. Alternatively, the MME maynotify a base station (cell) of the CSG registration situation of theuser equipment. “INITIAL CONTEXT SETUP REQUEST” may be used as therequest. Alternatively, “INITIAL CONTEXT SETUP REQUEST” may contain “CSGMembership Status”.

Then, the processes of Steps ST1408 to ST1416 shown in FIG. 14 describedabove are performed, and thereafter, the processes of Steps ST2300,ST2403, and ST2404 are performed. Then, in Step ST2602, the cellinquires the control unit of the base station about the configuration ofthe target CC determined in Step ST2303. The cell may inquire thecontrol unit of the base station about “CSG indication” and “CSG-ID” ofthe determined target CC. In this operation example, the cell1 being aPCell inquires the control unit of the base station A about “CSGindication” and “CSG-ID” of the cell2 determined as a target CC.

In Step ST2603, the control unit of the base station responds to theinquiry from the cell in Step ST2602. The control unit of the basestation may notify the cell of “CSG indication” and “CSG-ID” of theinquiry target cell. In this operation example, the control unit of thebase station A notifies the cell1 being a PCell of “CSG indication” and“CSG-ID” of the cell2 being an inquiry target cell.

In Step ST2604, the cell judges whether or not the target CC determinedin Step ST2303 has a CSG-ID. In other words, the cell judges whether ornot the target CC belongs to a CSG. In this judgment, the cell uses theresponse results to the inquiry, which have been received from thecontrol unit of the base station in Step ST2603.

In a case of judging that the target CC determined in Step ST2303 has aCSG-ID in Step ST2604, the cell moves to Step ST2605. In other words, ina case of judging that the target CC determined in Step ST2303 has aCSG-ID in Step ST2604, the cell judges that the target CC belongs to theCSG, and then moves to Step ST2605.

In a case of judging that the target CC determined in Step ST2303 doesnot have a CSG-ID in Step ST2604, the cell moves to Step ST2312. Inother words, in a case of judging that the target CC determined in StepST2303 does not have a CSG-ID in Step ST2604, the cell judges that thetarget CC does not belong to the CSG, and then moves to Step ST2312.

In Step ST2605, the cell judges whether or not the CSG indication of thetarget CC determined in Step ST2303 shows “TRUE”. In other words, thecell judges whether or not the access mode of the target CC is a closedaccess mode. In this judgment, the cell uses the response results to theinquiry, which have been received from the control unit of the basestation in Step ST2603.

In a case of judging that the CSG indication of the target CC determinedin Step ST2303 does not show “TRUE”, that is, shows “FALSE”, in StepST2605, the cell moves to Step ST2312. In other words, in a case ofjudging that the operation mode of the target CC determined in StepST2303 is an open access mode or hybrid access mode in Step ST2605, thecell moves to Step ST2312.

In a case of judging that the CSG indication of the target CC determinedin Step ST2303 shows “TRUE” in Step ST2605, the cell moves to StepST2606. In other words, in a case of judging that the operation mode ofthe target CC determined in Step ST2303 is a closed access mode in StepST2605, the cell moves to Step ST2606.

In Step ST2606, the cell judges whether or not the user equipment hasbeen registered with a CSG to which the cell being a target CCdetermined in the Step ST2303 belongs. As to the CSG to which the targetCC belongs in this judgment, the response results to the inquiry, whichhave been received from the control unit of the base station in StepST2603, are used. As to the CSG registration situation of the userequipment in this judgment, the notification received from the MME inStep ST2601 is used.

In a case of judging that the user equipment has been registered withthe CSG to which the target CC belongs in Step ST2606, the cell moves toStep ST2312. In a case of judging that the user equipment has beenunregistered with the CSG to which the target CC belongs in Step ST2606,the cell ends the process and moves to other process. The other processis not specific to the present invention, which is not described here.

Through the processes of Steps ST2604, ST2605, and ST2606, a cell (CC)that does not belong to a CSG, a cell (CC) operating in an open accessmode among the cells (CCs) belonging to the CSG, a cell (CC) operatingin a hybrid access mode among the cells (CCs) belonging to the CSG, or acell (CC) belonging to the same CSG as the CSG to which the userequipment has been registered among the cells (CCs) belonging to the CSGcan be configured or selected as a target CC, which is specific to thepresent modification. Alternatively, a cell (CC) that operates in aclosed access mode and belongs to a CSG with which the user equipmenthas been unregistered among the cells (CCs) belonging to the CSG cannotbe configured or selected as a target CC.

The PCell may select a target CC candidate cell before determining atarget CC and perform the processes of Steps ST2602 to ST2606 on thecandidate cell, and then perform the process of Step ST2303, thoughdifferent from the sequence shown in FIG. 26.

In Step ST2607, the cell judges whether or not a target CC can accepthandover. In a case of judging that the target CC determined in StepST2303 can accept handover in Step ST2607, the cell moves to StepST2312. In a case of judging that the target CC determined in StepST2303 cannot accept handover in Step ST2607, the cell ends the processand moves to other process. The other process is not specific to thepresent invention, which is not described here.

The situations regarding the processing load and resource use of thetarget CC and the like may be taken into consideration in the judgmentof Step ST2607. The following is disclosed as a specific example of themethod in which a PCell knows the situations regarding the processingload and resource use of another cell. The situations regarding theprocessing load, resource use, and the like may be included in theconfiguration of the own cell.

The second modification of the eighth embodiment described above canachieve the following effects as in the eighth embodiment. The operationas a communication system can be stabilized while improving a data rateusing carrier aggregation, which enables to appropriately provideservices.

While the present modification has mainly described a case in whichhandover is used in PCell change, the present modification is alsoapplicable to a case in which a reconfiguration is used in PCell change.

The present modification can be used in combination with the firstembodiment, second embodiment, first modification of the secondembodiment, third embodiment, fourth embodiment, fifth embodiment, firstmodification of the fifth embodiment, sixth embodiment, seventhembodiment, eighth embodiment, and first modification of the eighthembodiment described above.

Third Modification of Eighth Embodiment

A third modification of the eighth embodiment discloses another solutionto the same problem as that of the eighth embodiment. The presentmodification mainly describes a portion different from the solutions inthe eighth embodiment and the second modification of the eighthembodiment, and a portion not to be described is similar to the eighthembodiment and the second modification of the eighth embodiment.

In the present modification, the PCell being a source cell changes theaccess control method for a target CC depending on whether or not thetarget cell is provided by the same base station. Alternatively, thePCell being a source cell may change the access control method for atarget CC depending on whether or not the target cell is controlled bythe same control unit.

A specific example of the method in which a source cell judges whetheror not a target cell is provided by the same base station is similar tothat of the eighth embodiment, which is not described here.

Disclosed below is a specific example of the access control method for atarget CC in a case where the target cell is not provided by the samebase station as that of the source CC being a PCell. For example, asshown in FIG. 23 described above, the MME performs access control on atarget CC. This specific example is also given as a specific example ofthe access control method for a target CC in a case where the targetcell is not controlled by the same control unit as that of the source CCbeing a PCell.

Disclosed below is a specific example of the access control method for atarget CC in a case where a target cell is provided by the same basestation as that of the source CC being a PCell. If the target CCsatisfies the preset conditions, access control in PCell change isomitted. This specific example is also given as a specific example ofthe access control method for a target CC in a case where the targetcell is controlled by the same control unit as that of the source CCbeing a PCell.

The following three (1) to (3) are disclosed as specific examples of thepreset conditions.

(1) Case where access control has been performed on a target CC. Aspecific example of the case where access control has been performed isdescribed below. A target CC is selected from SCells. A target CC may beselected from access-controlled SCells. Specific examples of theaccess-controlled SCells include the SCells that are configured in thethird embodiment, fourth embodiment, fifth embodiment, sixth embodiment,or seventh embodiment described above.

(2) Case where a target CC is a cell (CC) that does not require accesscontrol. Specific examples of the cell that does not require accesscontrol include a cell (CC) that does not belong to a CSG, a cell (CC)operating in an open access mode among the cells (CCs) belonging to theCSG, and a cell (CC) operating in a hybrid access mode among the cells(CCs) belonging to the CSG. A method similar to that of the fourthembodiment described above can be used as a specific example of themethod in which a PCell knows whether or not another cell belongs to aCSG or knows an operation mode in a case where another cell belongs tothe CSG, which is not described here.

(3) Combination of (1) and (2) above.

If the target CC satisfies the preset other conditions, access controlin PCell change may be performed.

The following three (1) to (3) are disclosed as specific examples of theother conditions.

(1) Case where access control has not been performed on a target CC. Aspecific example of the case in which access control has not beenperformed is described below. The target CC is selected from cells otherthan the SCell. The target CC may be selected from cells other than theaccess-controlled SCell. The target CC may be selected from the SCellson which access control is not performed. Specific examples of the SCellon which access control has not been performed include the SCellconfigured in the second embodiment described above.

(2) Case where a target CC is a cell (CC) that requires access control.Specific examples of the cell that requires access control include acell (CC) belonging to a CSG. A target CC may be a cell (CC) operatingin a closed access mode among the cells (CCs) belonging to the CSG. Amethod similar to that of the fourth embodiment described above can beused as a specific example of the method in which a PCell knows whetheror not another cell belongs to a CSG and knows an operation mode in acase where another cell belongs to a CSG, which is not described here.

(3) Combination of (1) and (2) above.

Next, a specific example of a sequence of a communication system in thethird modification of the eighth embodiment is described with referenceto FIG. 27. FIG. 27 is a diagram showing an example of the sequence ofthe communication system in the third modification of the eighthembodiment. The processes of Steps ST1401 to ST1416 of FIG. 14 describedabove in the present modification are similar to those of the secondembodiment, which are not illustrated and described here. The sequenceshown in FIG. 27 is similar to the sequences shown in FIGS. 23 and 24,where the same steps are denoted by the same step numbers and commondescription is not given here.

This operation example describes a case in which a base station Aproviding a plurality of cells (CCs) including a cell and a cell2 ispresent, where the UE selects the cell of the base station A as the bestcell and camps on the cell to start communication, and thereafter, thecell2 is configured as a CC being a PCell change destination. A case inwhich access controlled has been performed on a target CC is disclosedas a specific example of the conditions under which access control isomitted in PCell change. A case in which a target CC is selected fromSCells is disclosed as a specific example in which access control hasbeen performed.

After the processes of Steps ST2400 to ST2402 are performed, theprocesses of Steps ST1401 to ST1416 shown in FIG. 14 described above areperformed, and then, the processes of Steps ST2300, ST2403, and ST2404are performed. Then, in Step ST2701, the cell judges whether or not thetarget CC determined in Step ST2303 is included in the SCells. In a caseof judging that the target CC determined in Step ST2303 is included inthe SCells in Step ST2701, the cell moves to Step ST2312. In a case ofjudging that the target CC determined in Step ST2303 is not included inthe SCells in Step ST2701, the cell moves to Step ST2702.

In Step ST2702, the cell performs access control in PCell change. Thefollowing four (1) to (4) are disclosed as specific examples of accesscontrol.

(1) Access control in PCell change that is disclosed in the eighthembodiment is performed. Specific examples thereof include the processesof Steps ST2405 to ST2311 shown in FIG. 24 described above.

(2) Access control in PCell change that is disclosed in the firstmodification of the eighth embodiment is performed. Specific examplesthereof include the processes of Steps ST2405 to ST2502 shown in FIG. 25described above.

(3) Access control in PCell change that is disclosed in the secondmodification of the eighth embodiment is performed. Specific examplesthereof include the processes of Steps ST2602 to ST2607 shown in FIG. 26described above.

(4) Combination of (1) to (3) above.

The third modification of the eighth embodiment above can achieve thefollowing effects in addition to the effects of the eighth embodimentand the second modification of the eighth embodiment. Control steps areomitted in the present modification, which enables to prevent controldelays in a communication system. In addition, a processing load of thebase station can be reduced. Further, consumption power of the basestation can be reduced.

While the present modification has mainly described a case in whichhandover is used in PCell change, the present modification is alsoapplicable to a case in which a reconfiguration is used in PCell change.

The present modification can be used in combination with the firstembodiment, second embodiment, first modification of the secondembodiment, third embodiment, fourth embodiment, fifth embodiment, firstmodification of the fifth embodiment, sixth embodiment, seventhembodiment, eighth embodiment, and first modification of the eighthembodiment described above.

As to the LTE-A, carrier aggregation between the eNB and RRH or betweenthe eNB and repeater is studied (see Non-Patent Document 1). Non-PatentDocument 1 does not describe the relationship between the eNB and RRH orthe relationship between the CSG to which the eNB and repeater belongand the CSG to which the user equipment belongs. As a result, theoperation of a communication system is not determined uniquely, leadingto a problem that services cannot be provided appropriately.

To tackle this problem, all the embodiments including the modificationsare applicable assuming that the cell (CC) in the present invention is aCC provided by an eNB, a CC included in an RRH, or a CC provided by arepeater. Accordingly, the operation as a communication system can bestabilized while improving a data rate using carrier aggregation betweenthe eNB and RRH or between the eNB and repeater, which enables toappropriately provided services.

As to the LTE-A, coordinated multiple point transmission and reception(CoMP) is studied (see Non-Patent Documents 6 and 7). The CoMP studiedrelates to the technique of improving the coverage of high data rates,improving a cell-edge throughput, and increasing a system throughputthrough transmission or reception coordinated among multiplegeographically separated points. The types of CoMP are classified intodownlink CoMP (DL CoMP) and uplink CoMP (UL CoMP).

The base stations (NB, eNB, HNB, HeNB), remote radio unit (RRU), remoteradio equipment (RRE), remote radio head (RRH), relay, and the like arestudied as specific examples of the multiple points, transmissionpoints, or reception points. The unit (cell) that performs coordinatedmultiple point transmission is referred to as a multi-point unit(multi-point cell), coordinated multiple point transmission andreception cooperation set (CoMP cooperation set), or coordinatedmultiple point transmission and reception transmission point(s) (CoMPtransmission point(s)).

Non-Patent Documents 6 and 7 do not describe the relationship betweenthe CSG to which the multiple points belong and the CSG to which theuser equipment belongs in the coordinated multiple point transmissionand reception cooperation set. Accordingly, the operation of acommunication system cannot be determined uniquely, leading to a problemthat services cannot be provided appropriately.

To tackle this problem, all the embodiments including the modificationsare applicable assuming that the cell (CC) in the present invention is atransmission point or reception point in CoMP. Accordingly, services canbe provided appropriately while improving the coverage of high datarates, improving a cell-edge throughput, and increasing a systemthroughput using the coordinated multiple point transmission andreception.

While the LTE-advanced system has been mainly described in therespective embodiments above, the communication system of the presentinvention is also applicable to other communication systems.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF REFERENCE SYMBOLS

-   -   71 user equipment device (UE), 72 base station device, 72-1 eNB,        72-2 Home-eNB, 73 MME/S-GW unit (MME unit), 74 HeNBGW, CC        component carrier, DL downlink, UL uplink.

The invention claimed is:
 1. A communication system comprising acommunication terminal device, a base station device configured toperform radio communication with said communication terminal device, anda host node device that restricts the connection between saidcommunication terminal device and said base station device, wherein saidbase station device provides a plurality of cells formed of componentcarriers having different frequencies, said base station deviceaggregating two or more cells of said plurality of cells andtransmitting and receiving component carriers of the aggregated cells inparallel to perform radio communication with said communication terminaldevice, said plurality of cells include a cell for specific subscribersthat specifies a connectable communication terminal device, uponestablishment of radio connection between any one of said plurality ofcells and said communication terminal device, a connected cellconfigures any of other cells as an aggregable cell that is allowed tobe aggregated with the connected cell, said connected cell being a cellin which radio connection with said communication terminal device hasbeen established, and upon said aggregable cell being configured by saidconnected cell: said host node device stops an operation of restrictingaccess to said aggregable cell; and said communication terminal devicestops an operation of restricting access to said aggregable cell basedon cell information being information related to said cell for specificsubscribers held in advance.
 2. The communication system according toclaim 1, wherein said connected cell configures, as said aggregablecell, a cell belonging to the same group of cells for specificsubscribers as that of the connected cell among said other cells.
 3. Thecommunication system according to claim 2, wherein said plurality ofcells are configured to belong to the same group of cells for specificsubscribers.
 4. The communication system according to claim 1, whereinsaid connected cell configures, as said aggregable cell, the remainingcells except for said cell for specific subscribers among said othercells.
 5. A communication system comprising a communication terminaldevice, a base station device configured to perform radio communicationwith said communication terminal device, and a host node device thatrestricts the connection between said communication terminal device andsaid base station device, wherein said base station device provides aplurality of cells formed of component carriers having differentfrequencies, said base station device aggregating two or more cells ofsaid plurality of cells and transmitting and receiving componentcarriers of the aggregated cells in parallel to perform radiocommunication with said communication terminal device, said plurality ofcells include a cell for specific subscribers that specifies aconnectable communication terminal device, upon establishment of radioconnection between any one of said plurality of cells and saidcommunication terminal device, a connected cell selects any one of saidother cells as a candidate cell being a candidate for aggregable cellthat is allowed to be aggregated with the connected cell and notifiessaid communication terminal device of information related to theselected candidate cell, said connected cell being a cell in which radioconnection with said communication terminal device has been established,upon notification of the information related to said candidate cell fromsaid connected cell, said communication terminal device judges whetheror not access to said candidate cell is allowed based on cellinformation related to said cell for specific subscribers held inadvance and notifies said connected cell of the judgment results, whenjudging that access to said candidate cell is allowed based on thejudgment results notified from said communication terminal device, saidconnected cell configures said candidate cell as said aggregable cell,and upon said aggregable cell being configured by said connected cell,said host node device stops an operation of restricting access to saidaggregable cell.
 6. The communication system according to claim 5,wherein said connected cell configures said candidate cell as saidaggregable cell based on a situation in which said communicationterminal device is allowed access to said candidate cell.